refactor(ffi-linkage): Phase 9.3 — purge 'foreign' from comments (src caps + examples + docs)

src/: ~21 capital-Foreign comments the case-sensitive verify grep missed
(Foreign-class→Runtime-class, Foreign path→Runtime path, Foreign decls→Extern decls,
FOREIGN function→extern function) across calls/inst/ffi_objc/jni_descriptor/emit_llvm/
c_import/lower.*/ops. src 'foreign' now = ONLY the hash_foreign token + 4 rejection
messages (9.0-delete targets). examples/*.sx comments → extern/runtime-class (1219
stdout regen; KEPT 1176). docs/inline-asm-design + debugger purged. Comments only —
no build impact. 9.0 ratified: DELETE hash_foreign token next.

examples/1349-ffi-objc-export-class.sx

@@ -1,6 +1,6 @@
 // Phase 3 (FFI-linkage) — postfix `export` on an `#objc_class` aggregate, the
 // explicit spelling for an sx-DEFINED runtime class (define + register). It is
-// the same lowering as a bare `#objc_class("X") { … }` with no `#foreign`;
+// the same lowering as a bare `#objc_class("X") { … }` with no `extern`;
 // `export` just makes the "I define this class" intent explicit (the dual of
 // `extern` for "I reference an existing class"). Mirrors 1339's defined class.