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.

src/backend/llvm/ops.zig

@@ -804,7 +804,7 @@ pub const Ops = struct {
         };
         const callee_needs_c_abi = callee_func.is_extern or callee_func.call_conv == .c;
         const callee_raw_ret = self.e.toLLVMType(callee_func.ret);
-        // Foreign string/?string returns receive one `char *` — never sret
+        // Extern string/?string returns receive one `char *` — never sret
         // (must mirror declareFunction's signature classification).
         const cstr_ret = self.e.cstrRetKind(callee_func);
         const callee_uses_sret = callee_needs_c_abi and cstr_ret == .none and self.e.needsByval(callee_func.ret, callee_raw_ret);