docs: automated documentation pipeline (per-symbol source → pages)

Replace the hardcoded landing page and minimal reference with a generated
documentation site driven by a single source of truth.

- docs/language/**: one file per symbol (93 keywords/types/builtins/namespace
  methods/operators/annotations), each with front-matter (id, kind, tokens,
  sig, tip) + description + a ```ludic example. Seeded by exploding the former
  inline SECTIONS list; these files are now the source of truth.
- docs/site/: site.json (editable hero/features/showcase/messaging, not
  hardcoded) + snippets/*.ludic (real programs shown on the landing page).
- tools/docgen/gen.py: generates index.html, api.html, ludic-highlight.js and
  symbols.json. The highlighter's symbol tables, hover tips and jump anchors
  are GENERATED from the per-symbol files — add a symbol and it is recognized,
  tipped and linked in every snippet automatically. Python stdlib only.
- tools/docgen/check.py: verifies the pages contract + that no snippet token
  links to a missing reference anchor.
- .forgejo/workflows/docs.yml: rebuilds and publishes to the pages branch on
  every push to main touching the docs sources.

Consumes the new Screen.*/Color.*/named-arg API and the 221-color palette.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/site/snippets/snake.ludic

@@ -0,0 +1,30 @@
+program Snake {
+  property Pos { x: int = 0, y: int = 0 }
+  property Seg { order: int = 0 }
+
+  const GRID_W: int = 20   const GRID_H: int = 15   const TILE: int = 16
+
+  var food_x: int = 14   var food_y: int = 7   var score: int = 0
+
+  handler Draw phase Render {
+    Screen.clear(Color.MidnightBlue)
+    # checkerboard field — a fresh, immutable gx/gy each pass
+    for gy in 0 .. GRID_H {
+      for gx in 0 .. GRID_W {
+        var tile_color = Color.Charcoal
+        if (gx + gy) % 2 == 0 { tile_color = Color.Gunmetal }
+        Screen.fill_rectangle(x: gx * TILE, y: gy * TILE, width: TILE, height: TILE, color: tile_color)
+      }
+    }
+    # the food, then every snake segment straight from the ECS
+    Screen.fill_rectangle(x: food_x * TILE + 3, y: food_y * TILE + 3, width: TILE - 6, height: TILE - 6, color: Color.Crimson)
+    for (p, s) in query [Pos, Seg] {
+      var seg_color = Color.LimeGreen
+      if s.order == 0 { seg_color = Color.MintGreen }        # brighter head
+      Screen.fill_rectangle(x: p.x * TILE + 1, y: p.y * TILE + 1, width: TILE - 2, height: TILE - 2, color: seg_color)
+    }
+    Screen.draw_text(x: 6, y: 4, text: "SCORE", color: Color.White, scale: 1)
+    Screen.draw_number(x: 52, y: 4, value: score, color: Color.Gold, scale: 1)
+    Screen.show()
+  }
+}