feat(types): option (some/none) safety type (#53)

Types phase 3 — the option/result safety pair. result/ok/err/try shipped in
#46; this adds its companion option:

- some(v)   -> option   (present value; any i32-width scalar)
- none()    -> option   (empty; no magic -1 sentinel)
- is_some / is_none -> bool
- unwrap_or(o, fallback) -> int

A heap %Option = { i32 present, i32 value }, bare builtins guarded by find_fn
(a user fn of the same name still wins), gated by g_uses_option so unused
programs compile byte-identically — same idiom as result.

Wired: emit_call codegen + %Option decl (emit_decl) + g_uses_option (emit_core),
reseeded seed, vocabulary sync (header/JetBrains/TextMate), builtin docs +
inventory, and a self-asserting example (examples/library/optionresult.ludic +
feat_case). All suites green incl. golden renders byte-identical and the
bootstrap fixpoint.

Tagged-union enums (variant payloads + binding match + exhaustiveness) are the
deep type-system feature, split out to #56.

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

docs/language/builtins/fn-is_some.md

@@ -0,0 +1,24 @@
+---
+id: fn-is_some
+name: is_some
+category: builtins
+kind: builtin
+tokens: is_some
+sig: is_some(o: option) -> bool
+tip: True when an option holds a value.
+order: 18
+---
+
+Returns true when an <code>option</code> holds a value (it is <a href="fn-some"><code>some</code></a>, not <a href="fn-none"><code>none</code></a>) — the guard before acting on an optional target or slot.
+
+Parameters:
+- `o` — the option to test
+
+```ludic
+program AI {
+  handler Step phase Update {
+    let target = none()
+    if is_some(target) { chase(unwrap_or(target, 0)) }
+  }
+}
+```