feat(stdlib): 2D Vector type + Vector.* namespace (issue #25)

Implement the Vec.* half of #25 under the proper (de-abbreviated) name
Vector, unblocking it with a self-contained value type instead of waiting
on the full #1 type system.

A Vector is two Q16.16 fixed components (x, y) packed into one i64 — a true
by-value type that lives in a register and never allocates (reuses the new
`long`/i64 support; llty maps `Vector` to i64). Fifteen operations, all
deterministic fixed-point reusing fx_mul/fx_div/fx_lerp and the @fn_fx_*
prelude: make/zero/x/y, add/sub/scale/dot, length/distance/normalize/lerp,
rotate/angle/from_angle.

New selfhost/emit_vector.ludic (wired into emit_ns_call + the frag list),
the `Vector` primitive type in llty and the grammars/LSP/JetBrains tokens,
docs (type-vector + 15 Vector.* pages + section), and a registered test.
Reseeded; C-free fixpoint holds; all suites green (45/25/29); site + check.py OK.

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

tools/editors/shared/ludic.tmLanguage.json

@@ -177,7 +177,7 @@
         { "name": "keyword.other.clause.ludic", "match": "\\b(phase|query|on)\\b" },
         { "name": "keyword.other.ludic", "match": "\\b(import|extern)\\b" },
         { "name": "storage.type.ludic", "match": "\\b(program|property|model|enum|ui|const|var|let|function|handler|entry|state)\\b" },
-        { "name": "support.type.primitive.ludic", "match": "\\b(int|long|fixed|bool|entity|string|pointer|byte|words|fixeds|pointers|void)\\b" },
+        { "name": "support.type.primitive.ludic", "match": "\\b(int|long|fixed|bool|entity|string|pointer|byte|words|fixeds|pointers|Vector|void)\\b" },
         { "name": "constant.language.boolean.ludic", "match": "\\b(true|false|null)\\b" },
         { "name": "constant.language.phase.ludic", "match": "\\b(Start|Input|FixedUpdate|Update|LateUpdate|Render)\\b" }
       ]