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/ecs/fn-world_count.md

@@ -0,0 +1,31 @@
+---
+id: fn-world_count
+name: world_count
+category: ecs
+kind: builtin
+tokens: world_count
+sig: world_count() -> int
+tip: The total number of live model instances in the world.
+order: 50
+---
+
+<code>world_count</code> returns the total number of live model instances in the world, as an `int` — a quick census without walking the world yourself. It takes no arguments and counts every spawned instance regardless of which properties it carries, so it is handy for a mod or debug overlay that wants a running tally of everything alive using the reflection ABI rather than a `query` loop. To resolve names to numeric ids for the other reflection calls, see `world_prop_id`; to read a specific instance's fields by id, see `world_get`.
+
+```ludic
+program Census {
+  property Position { column: int = 0, row: int = 0 }
+  model Enemy { Position }
+
+  handler SpawnEnemies phase Start {
+    spawn Enemy { Position { column: 3, row: 3 } }
+    spawn Enemy { Position { column: 9, row: 3 } }
+  }
+
+  handler DrawWorld phase Render {
+    Screen.clear(Color.MidnightBlue)
+    let alive = world_count()
+    Screen.draw_number(x: 8, y: 8, value: alive, color: Color.Gold, scale: 2)
+    Screen.show()
+  }
+}
+```