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-unwrap_or.md

@@ -0,0 +1,24 @@
+---
+id: fn-unwrap_or
+name: unwrap_or
+category: builtins
+kind: builtin
+tokens: unwrap_or
+sig: unwrap_or(o: option, fallback) -> int
+tip: The option value, or a fallback if empty.
+order: 20
+---
+
+Reads an <code>option</code>: returns its value when it is <a href="fn-some"><code>some</code></a>, or <code>fallback</code> when it is <a href="fn-none"><code>none</code></a>. The safe, one-line way to get a usable value out of an option without a separate branch.
+
+Parameters:
+- `o` — the option to read
+- `fallback` — the value to use when the option is empty
+
+```ludic
+program Config {
+  handler Step phase Update {
+    let volume = unwrap_or(none(), 100)     # default to 100
+  }
+}
+```