feat(ambient-ui): chat tab, action bar, persistent sidebar, tool args

Chat tab:
- Markdown rendering for user and assistant messages (react-markdown + remark-gfm)
- Tool call/result grouping into single collapsible blocks
- Extract last_assistant_message from system events when assistant payload is empty
- Dark mode support (semantic Tailwind tokens, no hardcoded hex)
- Scroll-to-top/bottom buttons with tooltips, matching old frontend pattern
- Input hint text below textarea, removed redundant phase badge from input

Action bar:
- Stop/Restart as primary buttons, Export/Delete in 3-dot dropdown menu
- Delete with confirmation dialog, navigates to fleet on success
- AlertDialog shadcn component added

Persistent chat sidebar:
- Pop-out button on Chat tab opens right-edge sidebar
- Sidebar persists across page navigation (context at dashboard layout level)
- Resizable by dragging, collapsible to narrow strip
- Session name in header links to session detail page
- Chat icon on fleet table rows opens sidebar
- Only one sidebar at a time, replacing on new session

Runner:
- Accumulate tool args from TOOL_CALL_ARGS events, push on TOOL_CALL_END
- Tool use messages now include full input arguments
- Updated tests for accumulation flow (22 passing)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jsell-rh

components/ambient-ui/src/adapters/sdk-sessions.ts

@@ -51,6 +51,10 @@ function createSdkSessionsAdapter(api: SessionAPI): SessionsPort {
       const session = await api.start(sessionId)
       return mapSdkSessionToDomain(session)
     },
+
+    async delete(sessionId: string): Promise<void> {
+      await api.delete(sessionId)
+    },
   }
 }