refactor(ffi-linkage): Phase 9.2a — rename runtime-class TYPE names → Runtime* (Decision 5)

Mechanical, collision-free PascalCase renames (object-model axis, not linkage):
ForeignClassDecl→RuntimeClassDecl, ForeignMethodDecl→RuntimeMethodDecl,
ForeignClassMember→RuntimeClassMember, ForeignFieldDecl→RuntimeFieldDecl,
ForeignRuntime→RuntimeKind, ForeignClassPrefix→RuntimeClassPrefix. Snapshot-neutral;
suite green (646/444). Remaining 9.2: snake_case state (foreign_class_map,
current_foreign_class, foreign_path [coupled to .sx hooks], the foreign_class_decl
union variant) + the parse/lower/resolve fn names + ForeignClassDecl.is_foreign flag.

src/ir/module.zig

@@ -74,7 +74,7 @@ pub const Module = struct {
     /// instance method without re-resolving types from the AST.
     pub const ObjcDefinedClassEntry = struct {
         name: []const u8,
-        decl: *const ast.ForeignClassDecl,
+        decl: *const ast.RuntimeClassDecl,
         methods: []const ObjcDefinedMethodEntry = &.{},
         /// Pre-resolved Obj-C runtime name of the parent class, so
         /// emit_llvm can pass it to `objc_getClass(parent)` /
@@ -146,14 +146,14 @@ pub const Module = struct {
     }
 
     /// Linear scan over sx-defined Obj-C classes.
-    pub fn lookupObjcDefinedClass(self: *const Module, name: []const u8) ?*const ast.ForeignClassDecl {
+    pub fn lookupObjcDefinedClass(self: *const Module, name: []const u8) ?*const ast.RuntimeClassDecl {
         for (self.objc_defined_class_cache.items) |entry| {
             if (std.mem.eql(u8, entry.name, name)) return entry.decl;
         }
         return null;
     }
 
-    pub fn appendObjcDefinedClass(self: *Module, name: []const u8, decl: *const ast.ForeignClassDecl) void {
+    pub fn appendObjcDefinedClass(self: *Module, name: []const u8, decl: *const ast.RuntimeClassDecl) void {
         self.objc_defined_class_cache.append(self.alloc, .{ .name = name, .decl = decl }) catch unreachable;
     }