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/structure/kw-fn.md

@@ -5,8 +5,34 @@ category: structure
 kind: keyword
 tokens: fn
 sig: fn name(a: T, b: T) -> R { … }
-tip: A function.
+tip: A function — reusable logic called positionally or with named arguments.
 order: 8
 ---
 
-A function. Call it positionally or with named arguments: <code>name(a: 1, b: 2)</code>.
+A <code>fn</code> declares a function: a reusable block of logic with typed parameters and a return type, written `-> R` (use `-> void` for one that returns nothing). Call it positionally, `heal(2, 10)`, or with named arguments, `heal(amount: 2, maximum: 10)`, which reads more clearly at the call site and is the house style. Functions live at program scope alongside handlers and may be called from any handler; they can `spawn`, run queries, and read program-scope state. Use them to factor out logic shared by several handlers so each handler stays short.
+
+Parameters:
+- `a`, `b` — the typed inputs; pass them positionally or by name at the call site
+
+```ludic
+program Healer {
+  property Health { current: int = 100, maximum: int = 100 }
+  model Player { Health }
+
+  fn heal(amount: int, maximum: int) -> int {
+    let restored = amount * 2
+    if restored > maximum { return maximum }
+    return restored
+  }
+
+  handler Boot phase Start {
+    spawn Hero { Health { current: 10, maximum: 100 } }
+  }
+
+  handler Recover phase Update {
+    for (health) in query [Health, {Player}] {
+      health.current = heal(amount: health.current, maximum: health.maximum)
+    }
+  }
+}
+```