refactor(ffi-linkage): Phase 9.2b — rename runtime-class fns + state → runtime_* / is_reference

The runtime-class object-model identifiers (Decision 5): parse/lower/find/resolve/
register/stamp fns Foreign→Runtime (parseRuntimeClassDecl, lowerRuntimeMethodCall,
findRuntimeMethodInChain, resolveRuntimeMethodReturnType, registerRuntimeClassDecl,
runtimeClassStructType, runtimeKindForOffset, …); state foreign_class_map→
runtime_class_map, current_foreign_class/_method→current_runtime_*, the
foreign_class_decl union variant→runtime_class_decl, foreign_method/static/instance/
class→runtime_*; and the reference-vs-define flag is_foreign→is_reference (+
is_foreign_eff→is_reference_eff) now that it only lives on RuntimeClassDecl.
Snapshot-neutral; suite green (646/444).

Remaining 9.2: the foreign_path family (coupled .sx hooks: jni_main_foreign_path_at
spans build.sx/bundle.sx/compiler_hooks.zig/specs.md) + the extern-ref validators
(checkForeignRefs etc. → Extern, linkage not runtime) + bare 'foreign' comments.

src/ir/module.zig

@@ -79,7 +79,7 @@ pub const Module = struct {
         /// Pre-resolved Obj-C runtime name of the parent class, so
         /// emit_llvm can pass it to `objc_getClass(parent)` /
         /// `objc_allocateClassPair(super, ...)` without walking the
-        /// sx-side foreign_class_map (which lives in lower.zig).
+        /// sx-side runtime_class_map (which lives in lower.zig).
         /// Defaults to "NSObject" when no `#extends` member is present.
         parent_objc_name: []const u8 = "NSObject",
     };