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>

changes/types-2d-ivec-rect.md

@@ -0,0 +1,13 @@
+bump: minor
+type: feat
+**2D value types — `IVec2` and `Rect` (#1, phase 1).** Two by-value spatial
+types that lower to packed integers, so they copy like scalars and never
+allocate. `IVec2` is an integer 2D vector (a pair of `int` packed into one
+`i64`) for tile and grid coordinates — `IVec2.make/zero/x/y/add/sub/scale/dot`,
+the grid distance `IVec2.manhattan`, `IVec2.equal`, and `IVec2.to_vector` to
+widen into the fixed-point `Vector`. `Rect` is an axis-aligned rectangle (four
+Q16.16 `fixed` components packed into one `i128`) for HUD boxes and hitboxes —
+`Rect.make/x/y/w/h`, the derived `Rect.right/bottom/center`, and the
+`Rect.contains` (point) and `Rect.intersects` (overlap) tests. Both are exact
+and deterministic, bit-identical on every platform, and complement the existing
+`Vector` and `Color` types that already cover phase 1's other 2D primitives.