ffi 3.2 C2: migrate uikit.sx Notifications + Bundle cluster

Second cluster: NSNotification, NSBundle, NSNotificationCenter move
from `#objc_call(T)(recv, "sel:", args)` to declarative
`#foreign #objc_class("Cls") { ... }` blocks.

Classes declared (alongside the C1 Foundation utility group):

- NSNotification        → userInfo (instance, returns *NSDictionary)
- NSBundle              → mainBundle (class), resourcePath (instance)
- NSNotificationCenter  → defaultCenter (class),
                          addObserver_selector_name_object (instance)

The 4-keyword `addObserver:selector:name:object:` selector derives
from the underscore-separated sx name via the default mangling rule
— no `#selector` override needed.

Cleanup wins:

- `objc_getClass("NSBundle")` and `objc_getClass("NSNotificationCenter")`
  call sites gone — class slots now populated by emit_llvm's
  `__sx_objc_class_init` constructor.
- `userInfo`'s return type is `*NSDictionary` directly, so the
  previous `*void → *NSDictionary` cast at the keyboard-frame
  callsite collapses.

166/166 tests; chess builds clean on macOS + iOS + Android via
`sx build main.sx`.

current/CHECKPOINT-FFI.md

@@ -553,8 +553,15 @@ foreign-class pointer at the dispatch site. The `objc_getClass(...)`
 calls for these classes are gone — the class slot is now populated
 by emit_llvm's `__sx_objc_class_init` constructor (Phase 3.1).
 
+Phase 3.2 C2 landed: notifications + bundle cluster migrated.
+NSNotification (`userInfo`), NSBundle (`mainBundle`, `resourcePath`),
+NSNotificationCenter (`defaultCenter`, `addObserver_selector_name_object`)
+declared as `#foreign #objc_class` blocks. The 4-keyword
+`addObserver:selector:name:object:` selector derives cleanly from
+the underscore-separated sx name (`addObserver_selector_name_object`).
+
 Open work:
-- **Phase 3 step 3.2 — C2..C5** — uikit.sx migration, one cluster
+- **Phase 3 step 3.2 — C3..C5** — uikit.sx migration, one cluster
   per commit, chess regression after each.
   test for the default-mangling table. Escape hatch for selectors
   that don't fit the underscore-split rule (e.g. `tableView_

library/modules/platform/uikit.sx

@@ -84,6 +84,22 @@ NSSet :: #foreign #objc_class("NSSet") {
     anyObject :: (self: *Self) -> *void;
 }
 
+// ── Notifications + Bundle (Phase 3.2 C2) ──────────────────────────────
+
+NSNotification :: #foreign #objc_class("NSNotification") {
+    userInfo :: (self: *Self) -> *NSDictionary;
+}
+
+NSBundle :: #foreign #objc_class("NSBundle") {
+    mainBundle   :: () -> *NSBundle;
+    resourcePath :: (self: *Self) -> *void;
+}
+
+NSNotificationCenter :: #foreign #objc_class("NSNotificationCenter") {
+    defaultCenter :: () -> *NSNotificationCenter;
+    addObserver_selector_name_object :: (self: *Self, observer: *void, sel: *void, name: *void, obj: *void);
+}
+
 // GLenum constants for renderbuffer/framebuffer setup that aren't in opengl.sx's
 // loader path (they live on the framework's symbol table directly).
 GL_RENDERBUFFER          :u32: 0x8D41;
@@ -304,9 +320,8 @@ uikit_refresh_safe_insets :: (plat: *UIKitPlatform) {
 
 uikit_chdir_to_bundle :: () {
     inline if OS != .ios { return; }
-    NSBundle := objc_getClass("NSBundle".ptr);
-    bundle := #objc_call(*void)(NSBundle, "mainBundle");
-    rsrc := #objc_call(*void)(bundle, "resourcePath");
+    bundle := NSBundle.mainBundle();
+    rsrc := bundle.resourcePath();
     if rsrc == null { return; }
     chdir(c_string(rsrc));
 }
@@ -388,9 +403,9 @@ uikit_keyboard_will_change_frame :: (self: *void, _cmd: *void, notification: *vo
     if g_uikit_plat == null { return; }
     plat := g_uikit_plat;
 
-    user_info_raw := #objc_call(*void)(notification, "userInfo");
-    if user_info_raw == null { return; }
-    user_info : *NSDictionary = xx user_info_raw;
+    notif : *NSNotification = xx notification;
+    user_info := notif.userInfo();
+    if user_info == null { return; }
 
     end_value_raw := user_info.objectForKey(ns_string("UIKeyboardFrameEndUserInfoKey".ptr));
     if end_value_raw == null { return; }
@@ -494,9 +509,8 @@ uikit_did_finish_launching :: (self: *void, _cmd: *void, app: *void, opts: *void
 
 uikit_subscribe_keyboard_notifications :: (delegate: *void) {
     inline if OS != .ios { return; }
-    NSNotificationCenter := objc_getClass("NSNotificationCenter".ptr);
-    center := #objc_call(*void)(NSNotificationCenter, "defaultCenter");
-    #objc_call(void)(center, "addObserver:selector:name:object:",
+    center := NSNotificationCenter.defaultCenter();
+    center.addObserver_selector_name_object(
         delegate,
         sel_registerName("sxKeyboardWillChangeFrame:".ptr),
         ns_string("UIKeyboardWillChangeFrameNotification".ptr),