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/events/kw-cancellable.md

@@ -0,0 +1,34 @@
+---
+id: kw-cancellable
+name: cancellable
+category: events
+kind: keyword
+tokens: cancellable
+sig: event cancellable Name { … }
+tip: Marks an event whose listeners may veto it with cancel.
+order: 50
+---
+
+`cancellable` marks an event as a <b>decision, not just a notification</b>. A plain event tells listeners something happened; a `cancellable` event is fired <b>before</b> an action so a listener can veto it by calling `cancel`. The caller reads the verdict back by using `emit` as an expression: it yields `0` when no listener vetoed and `1` when one did, so the action is applied only on `0`. This is the Bukkit / DOM `preventDefault` shape — observation becomes control — and a foreign mod vetoes the same way by setting the payload's trailing cancelled flag over the ABI.
+
+```ludic
+program CancellableExample {
+  event cancellable BeforeHurt { amount: int = 0 }
+
+  var current_health: int = 100
+
+  @On(BeforeHurt) handler AbsorbSmallHits { if amount <= 5 { cancel } }
+
+  handler TakeDamage phase Update {
+    if Input.key() == 'h' {
+      if emit BeforeHurt(amount: 3) == 0 { current_health = current_health - 3 }
+    }
+  }
+
+  handler DrawWorld phase Render {
+    Screen.clear(Color.MidnightBlue)
+    Screen.draw_number(x: 4, y: 4, value: current_health, color: Color.Crimson, scale: 1)
+    Screen.show()
+  }
+}
+```