docs(api): per-symbol pages, fuzzy search, deep token linking, hover cards

Rebuild the API Reference around one page per symbol and richer, verified content.

Pages & navigation
- One HTML page per symbol (kw-*, type-*, phase-*, screen-*, fn-*, annot-*, op-*)
  instead of a single scrolling page; namespace overview pages (ns-screen …
  ns-color) and a searchable index (api.html) with client-side fuzzy search.
- Sticky-header scroll offset (scroll-margin) so a jumped-to entry/param/color is
  never hidden, plus a flash highlight on the scrolled-to target.

Deep linking in every snippet & example
- Namespace members split: `Screen`→namespace page, `fill_rectangle`→method page;
  `Color`→palette page, `Charcoal`→its swatch — separately.
- Named arguments (`width:`) link to that parameter's anchor on the method page.
- Hover any token for a summary card built from the real API data (symbols.json).

Content & coverage
- Full authoritative surface documented from the compiler: every keyword, type,
  the 6 phases (Start/Input/FixedUpdate/Update/LateUpdate/Render, each its own
  page), all 22 annotations, namespace methods with parameter docs, builtins,
  the world_* reflection ABI, networking, operators — 155 symbols.
- Longer, clearer explanations; "model"/"model instance" terminology, not "entity";
  descriptive identifiers in every example (Position{column,row}, Velocity{delta_x,
  delta_y}, Health{current,maximum}, Player/Enemy) — no Pos/Seg/x/dx.
- Accuracy fixes from compiler ground-truth: world_count() takes no arg,
  world_query_next(property, cursor) arg order, event fields bind by name; dropped
  `when` and `module` (not in the self-hosted parser).

Tooling
- inventory.json + check.py: coverage guard (every symbol has a page), duplicate-
  token guard, and broken-link guard — fail CI so docs can't drift.
- validate.py: compiles every ```ludic example against bin/ludicc (158 compile).

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

docs/language/scenes/kw-on.md

@@ -5,8 +5,48 @@ category: scenes
 kind: keyword
 tokens: on
 sig: on enter { … }   on exit { … }
-tip: Hooks that fire when a scene becomes active or is left.
+tip: Scene lifecycle hooks that fire as a scene becomes active or is left.
 order: 2
 ---
 
-Hooks that fire when a scene becomes active or is left.
+`on` introduces a scene's lifecycle hooks: `on enter { … }` runs once when the scene becomes active, and `on exit { … }` runs once as it is left. They are hooks, <b>not phases</b> — the place for per-scene setup and teardown that has no equivalent in a mode register. The start scene's `on enter` fires at boot right after the `Start` phase; on a `become Other` the current scene's `on exit` runs, the active scene switches, then the new scene's `on enter` runs. Use `on enter` to spawn the models a scene needs and reset its counters, and `on exit` to tidy up before leaving.
+
+```ludic
+program SceneHookExample {
+  property Position { column: int = 0, row: int = 0 }
+  model Enemy { Position }
+
+  var elapsed_frames: int = 0
+
+  scene Overworld start {
+    layer World {
+      handler EnterBattle phase Update {
+        if Input.key() == 'b' { become Battle }
+      }
+      handler DrawWorld phase Render {
+        Screen.clear(Color.MidnightBlue)
+        Screen.show()
+      }
+    }
+  }
+
+  scene Battle {
+    on enter {
+      elapsed_frames = 0
+      spawn Enemy { Position { column: 8, row: 4 } }
+    }
+    on exit {
+      for (any_position) in query [Position, {Enemy}] { despawn self() }
+    }
+    layer Fight {
+      handler DrawBattle phase Render {
+        Screen.clear(Color.Crimson)
+        for (current_position) in query [Position, {Enemy}] {
+          Screen.fill_rectangle(x: current_position.column * 16, y: current_position.row * 16, width: 16, height: 16, color: Color.White)
+        }
+        Screen.show()
+      }
+    }
+  }
+}
+```