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>

tools/docgen/inventory.json

@@ -319,7 +319,9 @@
     "type-string",
     "type-void",
     "type-words",
-    "type-vector"
+    "type-vector",
+    "type-ivec2",
+    "type-rect"
   ],
   "world": [
     "world-get",
@@ -356,6 +358,31 @@
     "vector-angle",
     "vector-from_angle"
   ],
+  "ivec2": [
+    "ivec2-make",
+    "ivec2-zero",
+    "ivec2-x",
+    "ivec2-y",
+    "ivec2-add",
+    "ivec2-sub",
+    "ivec2-scale",
+    "ivec2-dot",
+    "ivec2-equal",
+    "ivec2-manhattan",
+    "ivec2-to_vector"
+  ],
+  "rect": [
+    "rect-make",
+    "rect-x",
+    "rect-y",
+    "rect-w",
+    "rect-h",
+    "rect-right",
+    "rect-bottom",
+    "rect-center",
+    "rect-contains",
+    "rect-intersects"
+  ],
   "duration": [
     "duration-seconds",
     "duration-minutes",