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/operators/op-assign.md

@@ -4,8 +4,16 @@ name: Assignment
 category: operators
 kind: operator
 sig: name = value
-tip: Assign to a var, a field, or an element.
+tip: Store into a var, a field, or an element — a statement, not an expression.
 order: 5
 ---
 
-Assign to a <code>var</code>, a field, or an element. Not an expression.
+Assignment stores a value into a target — a `var` binding, a property field, or a buffer/slice element — with `target = value`. The compound forms `+=`, `-=`, `*=`, and `/=` update in place, so `score += 1` means `score = score + 1`. Assignment is a <b>statement, not an expression</b>: it produces no value, so you cannot write `if x = 0` (use `==` for the test). Only a mutable target accepts it — assigning to a `let` or `const` binding is a compile error — though you may still mutate <b>through</b> an immutable binding that holds a record or slice.
+
+```ludic
+var score: int = 0
+score = 10
+score += 5
+let current_position = new_position()
+current_position.column = current_position.column + 1
+```