fix: chat functionality and extended thinking handling

- bundle/bundle.md: Add provider-anthropic with source URL and orchestrator config override
  to disable extended_thinking (foundation enables it by default, causes empty text
  responses for simple queries)
- Dockerfile: Add amplifier-module-provider-anthropic pip install for container
- backend/agui_adapter.py: Fix thinking block handling and empty text block rendering
  - Thinking blocks no longer fall through to text handler
  - Text blocks only emit START when actual content arrives
  - Handle amplifierd wire format (block_index/block_type, complete text in content_block:end)
- frontend/src/hooks/useChat.ts: Reset assistantId on TEXT_MESSAGE_END to prevent stale
  message IDs across turns
- tests/test_agui_adapter.py: Add extended thinking test coverage

Chat functionality now works end-to-end. Verified: login -> create session -> send message -> receive AI response visible in chat UI.

Generated with Amplifier

frontend/src/hooks/useChat.ts

@@ -95,7 +95,7 @@ export function useChat(sessionId: string | null) {
               break
             }
             case 'TEXT_MESSAGE_END': {
-              // no-op
+              assistantId = null
               break
             }
             case 'TOOL_CALL_START': {