feat(plotly): implement gauge-basic (#9531)

## Implementation: `gauge-basic` - python/plotly

Implements the **python/plotly** version of `gauge-basic`.

**File:** `plots/gauge-basic/implementations/python/plotly.py`

**Parent Issue:** #857

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/28476584859)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/gauge-basic/implementations/python/plotly.py

@@ -1,7 +1,7 @@
 """ anyplot.ai
 gauge-basic: Basic Gauge Chart
-Library: plotly 6.7.0 | Python 3.14.4
-Quality: 94/100 | Updated: 2026-04-25
+Library: plotly 6.8.0 | Python 3.13.14
+Quality: 94/100 | Updated: 2026-06-30
 """
 
 import os
@@ -17,42 +17,53 @@
 INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
 INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
 
-# Okabe-Ito colorblind-safe stand-ins for the red/amber/green convention
-ZONE_LOW = "#AE3030"  # imprint red — bad
-ZONE_MID = "#DDCC77"  # imprint amber — caution
-ZONE_HIGH = "#009E73"  # imprint green — good
+# Imprint palette zone colors: red=bad, amber=caution, green=good
+ZONE_LOW = "#AE3030"  # Imprint matte red — At Risk
+ZONE_MID = "#DDCC77"  # Imprint amber — On Track
+ZONE_HIGH = "#009E73"  # Imprint brand green — Exceeds Target
 
 # Data — Sales target achievement for the quarter
 value = 72
 min_value = 0
 max_value = 100
 thresholds = [30, 70]
 
+goal = thresholds[1]
+
 # Plot
 fig = go.Figure(
     go.Indicator(
-        mode="gauge+number",
+        mode="gauge+number+delta",
         value=value,
-        number={"font": {"size": 96, "color": INK}, "suffix": "%"},
+        number={"font": {"size": 48, "color": INK, "family": "Arial"}, "suffix": "%"},
+        delta={
+            "reference": goal,
+            "relative": False,
+            "valueformat": "+.0f",
+            "suffix": "pp vs. goal",
+            "font": {"size": 13, "color": INK, "family": "Arial"},
+            "increasing": {"color": ZONE_HIGH},
+            "decreasing": {"color": ZONE_LOW},
+        },
         title={
             "text": (
                 "<b>Sales Target Achievement</b>"
-                f"<br><span style='font-size:22px;color:{INK_SOFT}'>"
-                "gauge-basic · plotly · anyplot.ai</span>"
+                f"<br><span style='font-size:11px;color:{INK_SOFT}'>"
+                "gauge-basic · python · plotly · anyplot.ai</span>"
             ),
-            "font": {"size": 32, "color": INK},
+            "font": {"size": 16, "color": INK, "family": "Arial"},
         },
         gauge={
             "shape": "angular",
             "axis": {
                 "range": [min_value, max_value],
-                "tickwidth": 2,
+                "tickwidth": 1,
                 "tickcolor": INK_SOFT,
-                "tickfont": {"size": 18, "color": INK_SOFT},
+                "tickfont": {"size": 10, "color": INK_SOFT, "family": "Arial"},
                 "ticksuffix": "%",
                 "dtick": 10,
             },
-            # Slim needle-style indicator so the zone colors stay visible
+            # Slim needle keeps zone colors fully visible
             "bar": {"color": INK, "thickness": 0.06, "line": {"color": INK, "width": 0}},
             "bgcolor": ELEVATED_BG,
             "borderwidth": 1,
@@ -62,18 +73,19 @@
                 {"range": [thresholds[0], thresholds[1]], "color": ZONE_MID},
                 {"range": [thresholds[1], max_value], "color": ZONE_HIGH},
             ],
-            "threshold": {"line": {"color": INK, "width": 5}, "thickness": 0.95, "value": value},
+            "threshold": {"line": {"color": INK, "width": 3}, "thickness": 0.95, "value": value},
         },
         domain={"x": [0.05, 0.95], "y": [0.30, 0.95]},
     )
 )
 
-# Layout — page surface + zone legend + target-exceeded callout
+# Layout — page surface + zone legend + callout
 fig.update_layout(
     paper_bgcolor=PAGE_BG,
     plot_bgcolor=PAGE_BG,
     font={"family": "Arial", "color": INK},
-    margin={"l": 80, "r": 80, "t": 140, "b": 120},
+    autosize=False,
+    margin={"l": 40, "r": 40, "t": 70, "b": 60},
     annotations=[
         # Zone legend row — three color-coded chips below the gauge
         {
@@ -82,56 +94,56 @@
             "xref": "paper",
             "yref": "paper",
             "text": (
-                f"<span style='color:{ZONE_LOW};font-size:24px'>●</span>  "
+                f"<span style='color:{ZONE_LOW};font-size:13px'>●</span>  "
                 f"<b>At Risk</b>  "
                 f"<span style='color:{INK_MUTED}'>0–30%</span>"
             ),
             "showarrow": False,
-            "font": {"size": 18, "color": INK},
+            "font": {"size": 12, "color": INK, "family": "Arial"},
         },
         {
             "x": 0.50,
             "y": 0.14,
             "xref": "paper",
             "yref": "paper",
             "text": (
-                f"<span style='color:{ZONE_MID};font-size:24px'>●</span>  "
+                f"<span style='color:{ZONE_MID};font-size:13px'>●</span>  "
                 f"<b>On Track</b>  "
                 f"<span style='color:{INK_MUTED}'>30–70%</span>"
             ),
             "showarrow": False,
-            "font": {"size": 18, "color": INK},
+            "font": {"size": 12, "color": INK, "family": "Arial"},
         },
         {
             "x": 0.80,
             "y": 0.14,
             "xref": "paper",
             "yref": "paper",
             "text": (
-                f"<span style='color:{ZONE_HIGH};font-size:24px'>●</span>  "
+                f"<span style='color:{ZONE_HIGH};font-size:13px'>●</span>  "
                 f"<b>Exceeds Target</b>  "
                 f"<span style='color:{INK_MUTED}'>70–100%</span>"
             ),
             "showarrow": False,
-            "font": {"size": 18, "color": INK},
+            "font": {"size": 12, "color": INK, "family": "Arial"},
         },
-        # Target-exceeded callout — emphasises the threshold-crossing story
+        # Target-exceeded callout — immediate data story
         {
             "x": 0.5,
-            "y": 0.02,
+            "y": 0.03,
             "xref": "paper",
             "yref": "paper",
             "text": "<b>✓ Target Exceeded</b>  ·  72% surpasses the 70% goal",
             "showarrow": False,
-            "font": {"size": 22, "color": ZONE_HIGH},
+            "font": {"size": 12, "color": ZONE_HIGH, "family": "Arial"},
             "bgcolor": ELEVATED_BG,
             "bordercolor": ZONE_HIGH,
-            "borderwidth": 2,
-            "borderpad": 12,
+            "borderwidth": 1,
+            "borderpad": 6,
         },
     ],
 )
 
 # Save
-fig.write_image(f"plot-{THEME}.png", width=1600, height=900, scale=3)
+fig.write_image(f"plot-{THEME}.png", width=800, height=450, scale=4)
 fig.write_html(f"plot-{THEME}.html", include_plotlyjs="cdn")