web(coder UI): ChatInput migration + Thinking render + DiffPanel route fix

Bundles in-progress working-tree UI work not authored this session (CoderPane ChatInput migration, AgentComposerBar/CoderMessageList/tab-bar/sidebar/pane refinements, provider icons) with this session's changes to the same files: MessageBubble renders a collapsible 'Thinking' block from reasoning_text/reasoning_parts (surfacing ACP agent_thought_chunk + native reasoning), and the DiffPanel approve/reject calls are repointed to the real /api/coder/pending/:id/apply and /reject routes (the old /sessions/:id/pending/:id/approve|reject paths did not exist).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/hooks/sessionEvents.ts

@@ -162,6 +162,10 @@ export interface ChatStatusEvent {
   reason?: ErrorReason;
 }
 
+export interface RefetchMessagesEvent {
+  type: 'refetch_messages';
+}
+
 export type SessionEvent =
   | SessionRenamedEvent
   | ProjectCreatedEvent
@@ -186,7 +190,8 @@ export type SessionEvent =
   | ProjectArchivedEvent
   | ProjectUnarchivedEvent
   | ProjectUpdatedEvent
-  | ChatStatusEvent;
+  | ChatStatusEvent
+  | RefetchMessagesEvent;
 type Listener = (event: SessionEvent) => void;
 
 const listeners = new Set<Listener>();