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/components/MobileTabSwitcher.tsx

@@ -273,7 +273,7 @@ export function MobileTabSwitcher({
                       <MoreHorizontal size={14} />
                     </button>
                   </DropdownMenuTrigger>
-                  <DropdownMenuContent align="end">
+                  <DropdownMenuContent align="end" className="min-w-44">
                     {chat && (
                       <DropdownMenuItem onSelect={() => startRename(chat.id, chat.name)}>
                         <Edit2 size={14} /> Rename chat