feat(types): IVec2 + Rect 2D value types (#1)

Phase 1 of the fuller type-system proposal: two by-value spatial types
that lower to packed integers (no heap, copy like scalars).

- IVec2 — integer 2D vector, a pair of int packed into one i64, for tile
  and grid coordinates: make/zero/x/y/add/sub/scale/dot, the grid distance
  manhattan, equal, and to_vector (widen into the fixed-point Vector).
- Rect — axis-aligned rectangle, four Q16.16 fixed components packed into
  one i128, for HUD boxes and hitboxes: make/x/y/w/h, the derived
  right/bottom/center, and the contains (point) / intersects (overlap) tests.

Both are exact and deterministic, bit-identical on every platform. Vector
and Color already cover phase 1's other 2D primitives.

Wired end to end: emit_core llty (IVec2->i64, Rect->i128), emit_call
dispatch, the FRAGS list + reseeded seed, a selfhost test (types2d),
per-symbol docs + type pages + inventory, and the vocabulary/editor sync
(header, JetBrains, TextMate, LSP).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/rect/rect-bottom.md

@@ -0,0 +1,22 @@
+---
+id: rect-bottom
+name: Rect.bottom
+category: rect
+kind: namespace-method
+tokens: Rect.bottom
+sig: Rect.bottom(r) -> fixed
+tip: The bottom edge, y + h.
+order: 6
+ns: Rect
+member: bottom
+---
+
+Returns the bottom edge, <code>y + h</code> — the y coordinate just below the rectangle.
+
+```ludic
+program Demo {
+  handler Step phase Update {
+    let base = Rect.bottom(hud)
+  }
+}
+```