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/builtins/fn-fx.md

@@ -1,12 +1,26 @@
 ---
 id: fn-fx
-name: fx / flr
+name: fx
 category: builtins
 kind: builtin
-tokens: fx flr
-sig: fx(n) -> fixed / flr(x) -> int
-tip: Convert between int and fixed-point.
-order: 10
+tokens: fx
+sig: fx(n) -> fixed
+tip: Lift an integer into a Q16.16 fixed-point value.
+order: 50
 ---
 
-Convert between int and fixed-point.
+Converts an integer into a <code>fixed</code> value (Ludic's Q16.16 fixed-point type), so it can take part in fractional arithmetic. Ludic has no floating point; <code>fixed</code> is how you carry sub-pixel precision for smooth movement and physics-like accumulation. Use <code>fx</code> when you need to combine an <code>int</code> with fixed-point values or divide to get a fraction — for example <code>fx(1) / fx(4)</code> is <code>0.25</code>. Convert back to a whole number for drawing with <code>flr</code>.
+
+Parameters:
+- `n` — the integer to lift into fixed-point
+
+```ludic
+program SmoothAccumulate {
+  handler ComputeStep phase Start {
+    let full_speed = fx(3)
+    let half_speed = full_speed / fx(2)
+    let two_steps = half_speed + half_speed
+    print(flr(two_steps))
+  }
+}
+```