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/useSidebar.ts

@@ -184,6 +184,7 @@ function applyEvent(prev: SidebarResponse, event: import('./sessionEvents').Sess
     case 'chat_unarchived':
     case 'chat_deleted':
     case 'chat_status':
+    case 'refetch_messages':
       return prev;
     case 'project_archived': {
       const next = prev.projects.filter((p) => p.id !== event.project_id);