feat(letsplot): implement renko-basic (#3331)

## Implementation: `renko-basic` - letsplot

Implements the **letsplot** version of `renko-basic`.

**File:** `plots/renko-basic/implementations/letsplot.py`

**Parent Issue:** #3294

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20823195596)*

---------

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

Author: github-actions[bot]

plots/renko-basic/implementations/letsplot.py

@@ -0,0 +1,104 @@
+"""pyplots.ai
+renko-basic: Basic Renko Chart
+Library: lets-plot | Python 3.13
+Quality: pending | Created: 2026-01-08
+"""
+
+import numpy as np
+import pandas as pd
+from lets_plot import *
+
+
+LetsPlot.setup_html()
+
+# Generate sample price data (simulating stock prices)
+np.random.seed(42)
+n_days = 200
+dates = pd.date_range("2024-01-01", periods=n_days, freq="D")
+# Simulate price with random walk
+returns = np.random.normal(0.001, 0.02, n_days)
+prices = 100 * np.cumprod(1 + returns)
+
+# Renko chart parameters
+brick_size = 2.0  # $2 brick size
+
+# Calculate Renko bricks
+bricks = []
+current_price = prices[0]
+brick_start = (current_price // brick_size) * brick_size
+direction = None  # 1 for up, -1 for down
+
+for price in prices:
+    while True:
+        if direction is None:
+            # Initial direction
+            if price >= brick_start + brick_size:
+                bricks.append({"bottom": brick_start, "top": brick_start + brick_size, "direction": 1})
+                brick_start += brick_size
+                direction = 1
+            elif price <= brick_start - brick_size:
+                bricks.append({"bottom": brick_start - brick_size, "top": brick_start, "direction": -1})
+                brick_start -= brick_size
+                direction = -1
+            else:
+                break
+        elif direction == 1:
+            # Currently in uptrend
+            if price >= brick_start + brick_size:
+                bricks.append({"bottom": brick_start, "top": brick_start + brick_size, "direction": 1})
+                brick_start += brick_size
+            elif price <= brick_start - 2 * brick_size:
+                # Reversal requires 2 bricks in opposite direction
+                brick_start -= brick_size
+                bricks.append({"bottom": brick_start - brick_size, "top": brick_start, "direction": -1})
+                brick_start -= brick_size
+                direction = -1
+            else:
+                break
+        else:
+            # Currently in downtrend
+            if price <= brick_start - brick_size:
+                bricks.append({"bottom": brick_start - brick_size, "top": brick_start, "direction": -1})
+                brick_start -= brick_size
+            elif price >= brick_start + 2 * brick_size:
+                # Reversal requires 2 bricks in opposite direction
+                brick_start += brick_size
+                bricks.append({"bottom": brick_start, "top": brick_start + brick_size, "direction": 1})
+                brick_start += brick_size
+                direction = 1
+            else:
+                break
+
+# Create DataFrame for plotting
+brick_df = pd.DataFrame(bricks)
+brick_df["x"] = range(len(brick_df))
+brick_df["color"] = brick_df["direction"].map({1: "Bullish", -1: "Bearish"})
+# Add small gap between bricks
+gap = 0.1
+brick_df["xmin"] = brick_df["x"] - 0.4 + gap / 2
+brick_df["xmax"] = brick_df["x"] + 0.4 - gap / 2
+
+# Create the plot
+plot = (
+    ggplot(brick_df)
+    + geom_rect(aes(xmin="xmin", xmax="xmax", ymin="bottom", ymax="top", fill="color"), color="white", size=0.5)
+    + scale_fill_manual(values={"Bullish": "#22C55E", "Bearish": "#EF4444"})
+    + labs(title="renko-basic · letsplot · pyplots.ai", x="Brick Index", y="Price ($)", fill="Direction")
+    + theme_minimal()
+    + theme(
+        plot_title=element_text(size=24),
+        axis_title=element_text(size=20),
+        axis_text=element_text(size=16),
+        legend_text=element_text(size=16),
+        legend_title=element_text(size=18),
+        panel_grid_major=element_line(color="#E5E5E5", size=0.5),
+        panel_grid_minor=element_blank(),
+    )
+    + ggsize(1600, 900)
+)
+
+# Save as PNG (scale 3x for 4800x2700)
+ggsave(plot, "plot.png", path=".", scale=3)
+
+# Save as HTML for interactivity
+ggsave(plot, "plot.html", path=".")

plots/renko-basic/metadata/letsplot.yaml

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+# Per-library metadata for letsplot implementation of renko-basic
+# Auto-generated by impl-generate.yml
+
+library: letsplot
+specification_id: renko-basic
+created: '2026-01-08T16:12:05Z'
+updated: '2026-01-08T16:12:05Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20823195596
+issue: 3294
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/renko-basic/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/renko-basic/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/renko-basic/letsplot/plot.html
+quality_score: null
+review:
+  strengths: []
+  weaknesses: []