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/jetbrains/src/main/kotlin/io/ludic/ide/LudicTokens.kt

@@ -52,7 +52,7 @@ object LudicVocabulary {
         "enable", "disable", "match", "machine", "state", "become", "where",
         "and", "or", "not", "break", "continue", "new", "emit", "cancel"
     )
-    val PRIMITIVES = setOf("int", "long", "fixed", "bool", "entity", "string", "pointer", "byte", "words", "fixeds", "pointers", "void")
+    val PRIMITIVES = setOf("int", "long", "fixed", "bool", "entity", "string", "pointer", "byte", "words", "fixeds", "pointers", "Vector", "void")
     val PHASES = setOf("Start", "Input", "FixedUpdate", "Update", "LateUpdate", "Render")
     val WIDGETS = setOf("panel", "col", "row", "label", "button", "image", "spacer")