feat(letsplot): implement network-transport-static (#3600)

## Implementation: `network-transport-static` - letsplot

Implements the **letsplot** version of `network-transport-static`.

**File:** `plots/network-transport-static/implementations/letsplot.py`

**Parent Issue:** #3463

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20868910557)*

---------

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/network-transport-static/implementations/letsplot.py

@@ -0,0 +1,202 @@
+""" pyplots.ai
+network-transport-static: Static Transport Network Diagram
+Library: letsplot 4.8.2 | Python 3.13.11
+Quality: 90/100 | Created: 2026-01-09
+"""
+
+import numpy as np
+import pandas as pd
+from lets_plot import (
+    LetsPlot,
+    aes,
+    arrow,
+    coord_fixed,
+    element_text,
+    geom_point,
+    geom_segment,
+    geom_text,
+    ggplot,
+    ggsave,
+    ggsize,
+    labs,
+    layer_tooltips,
+    scale_color_manual,
+    scale_x_continuous,
+    scale_y_continuous,
+    theme,
+    theme_void,
+)
+
+
+LetsPlot.setup_html()
+
+# Data: Regional rail network with stations and routes
+np.random.seed(42)
+
+# Station data with x, y coordinates (positioned like a simplified rail map)
+stations = [
+    {"id": "A", "label": "Central", "x": 0.5, "y": 0.5},
+    {"id": "B", "label": "North", "x": 0.5, "y": 0.88},
+    {"id": "C", "label": "East", "x": 0.82, "y": 0.5},
+    {"id": "D", "label": "South", "x": 0.5, "y": 0.12},
+    {"id": "E", "label": "West", "x": 0.18, "y": 0.5},
+    {"id": "F", "label": "Airport", "x": 0.82, "y": 0.82},
+    {"id": "G", "label": "University", "x": 0.18, "y": 0.82},
+    {"id": "H", "label": "Harbor", "x": 0.82, "y": 0.18},
+    {"id": "I", "label": "Tech Park", "x": 0.18, "y": 0.18},
+    {"id": "J", "label": "Stadium", "x": 0.66, "y": 0.32},
+]
+
+# Route data: train connections with times
+# Includes multiple routes between same stations to demonstrate curved edges
+routes = [
+    # Express routes (RE) - Central hub connections
+    {"source": "A", "target": "B", "route_id": "RE1", "depart": "06:15", "arrive": "06:35", "type": "Express"},
+    {"source": "A", "target": "C", "route_id": "RE2", "depart": "06:30", "arrive": "06:55", "type": "Express"},
+    {"source": "A", "target": "D", "route_id": "RE3", "depart": "07:00", "arrive": "07:25", "type": "Express"},
+    {"source": "A", "target": "E", "route_id": "RE4", "depart": "07:15", "arrive": "07:40", "type": "Express"},
+    # Regional routes (RB) - Connecting outer stations
+    {"source": "B", "target": "F", "route_id": "RB1", "depart": "07:00", "arrive": "07:20", "type": "Regional"},
+    {"source": "B", "target": "G", "route_id": "RB2", "depart": "07:30", "arrive": "07:55", "type": "Regional"},
+    {"source": "C", "target": "F", "route_id": "RB3", "depart": "08:00", "arrive": "08:25", "type": "Regional"},
+    {"source": "C", "target": "H", "route_id": "RB4", "depart": "08:15", "arrive": "08:40", "type": "Regional"},
+    {"source": "D", "target": "H", "route_id": "RB5", "depart": "08:30", "arrive": "08:55", "type": "Regional"},
+    {"source": "D", "target": "I", "route_id": "RB6", "depart": "09:00", "arrive": "09:30", "type": "Regional"},
+    {"source": "E", "target": "G", "route_id": "RB7", "depart": "09:15", "arrive": "09:40", "type": "Regional"},
+    {"source": "E", "target": "I", "route_id": "RB8", "depart": "09:30", "arrive": "09:55", "type": "Regional"},
+    # Local routes (S) - Short connections, including multiple routes to same destination
+    {"source": "C", "target": "J", "route_id": "S1", "depart": "10:00", "arrive": "10:12", "type": "Local"},
+    {"source": "J", "target": "H", "route_id": "S2", "depart": "10:15", "arrive": "10:30", "type": "Local"},
+    {"source": "A", "target": "J", "route_id": "S3", "depart": "10:30", "arrive": "10:50", "type": "Local"},
+    # Second Express route A→C to demonstrate offset edges
+    {"source": "A", "target": "C", "route_id": "RE5", "depart": "12:30", "arrive": "12:55", "type": "Express"},
+]
+
+# Create DataFrames
+stations_df = pd.DataFrame(stations)
+
+# Track route counts between station pairs for offset calculation
+route_counts = {}
+for r in routes:
+    key = (r["source"], r["target"])
+    route_counts[key] = route_counts.get(key, 0) + 1
+
+route_index = {}
+
+# Build edge DataFrame with source/target coordinates and curve offsets
+station_coords = {s["id"]: (s["x"], s["y"]) for s in stations}
+edges_data = []
+for r in routes:
+    src_x, src_y = station_coords[r["source"]]
+    tgt_x, tgt_y = station_coords[r["target"]]
+
+    # Track index for this station pair
+    key = (r["source"], r["target"])
+    idx = route_index.get(key, 0)
+    route_index[key] = idx + 1
+    total = route_counts[key]
+
+    # Shorten edges slightly so arrows don't overlap nodes
+    dx, dy = tgt_x - src_x, tgt_y - src_y
+    length = np.sqrt(dx**2 + dy**2)
+    offset = 0.045 / length if length > 0 else 0
+
+    # Calculate perpendicular offset for curved/offset edges
+    perp_x = -dy / length if length > 0 else 0
+    perp_y = dx / length if length > 0 else 0
+
+    # Apply perpendicular offset for multiple routes between same stations (increased for visibility)
+    if total > 1:
+        curve_offset = 0.05 * (idx - (total - 1) / 2)
+    else:
+        curve_offset = 0
+
+    # Offset labels perpendicular to edge direction (increased for clarity)
+    label_offset = 0.055
+
+    edges_data.append(
+        {
+            "x": src_x + dx * offset + perp_x * curve_offset,
+            "y": src_y + dy * offset + perp_y * curve_offset,
+            "xend": tgt_x - dx * offset + perp_x * curve_offset,
+            "yend": tgt_y - dy * offset + perp_y * curve_offset,
+            "route_id": r["route_id"],
+            "depart": r["depart"],
+            "arrive": r["arrive"],
+            "label": f"{r['route_id']} | {r['depart']} → {r['arrive']}",
+            "type": r["type"],
+            "mid_x": (src_x + tgt_x) / 2 + perp_x * (label_offset + curve_offset),
+            "mid_y": (src_y + tgt_y) / 2 + perp_y * (label_offset + curve_offset),
+            "source_station": next(s["label"] for s in stations if s["id"] == r["source"]),
+            "target_station": next(s["label"] for s in stations if s["id"] == r["target"]),
+        }
+    )
+
+edges_df = pd.DataFrame(edges_data)
+
+# Color palette for route types
+route_colors = {"Express": "#306998", "Regional": "#B8860B", "Local": "#2E8B57"}
+
+# Create tooltip specs for interactive hover
+edge_tooltips = (
+    layer_tooltips()
+    .title("@route_id")
+    .line("@source_station → @target_station")
+    .line("Departs: @depart")
+    .line("Arrives: @arrive")
+    .line("Type: @type")
+)
+
+station_tooltips = layer_tooltips().title("@label").line("Station ID: @id")
+
+# Create the plot with interactive tooltips
+plot = (
+    ggplot()
+    # Draw edges as segments with arrows and tooltips
+    + geom_segment(
+        aes(x="x", y="y", xend="xend", yend="yend", color="type"),
+        data=edges_df,
+        size=1.8,
+        alpha=0.85,
+        arrow=arrow(angle=25, length=12, type="closed"),
+        tooltips=edge_tooltips,
+    )
+    # Draw edge labels (route and times) - larger for readability
+    + geom_text(aes(x="mid_x", y="mid_y", label="label", color="type"), data=edges_df, size=6)
+    # Draw station nodes with tooltips
+    + geom_point(
+        aes(x="x", y="y"),
+        data=stations_df,
+        size=12,
+        color="white",
+        shape=21,
+        fill="#303030",
+        stroke=2.5,
+        tooltips=station_tooltips,
+    )
+    # Draw station labels (adjusted position to avoid edge label overlap)
+    + geom_text(
+        aes(x="x", y="y", label="label"), data=stations_df, size=9, color="#202020", fontface="bold", nudge_y=-0.055
+    )
+    # Color scale for route types
+    + scale_color_manual(values=route_colors, name="Route Type")
+    # Styling
+    + labs(title="network-transport-static · letsplot · pyplots.ai", x="", y="")
+    + theme_void()
+    + theme(
+        plot_title=element_text(size=24, face="bold", hjust=0.5),
+        legend_position="right",
+        legend_title=element_text(size=16),
+        legend_text=element_text(size=14),
+    )
+    + scale_x_continuous(limits=[0, 1])
+    + scale_y_continuous(limits=[0, 1])
+    + coord_fixed(ratio=1)
+    + ggsize(1600, 900)
+)
+
+# Save as PNG (scale 3x for 4800x2700)
+ggsave(plot, "plot.png", scale=3, path=".")
+
+# Save as HTML for interactivity (tooltips work in HTML)
+ggsave(plot, "plot.html", path=".")