add tool calling, SQLite persistence, group chat, image vision, voice transcription

Major features:
- OpenAI function calling with tool call loop (streaming SSE parsing)
- Built-in tools: spawn_agent (async claude -p), agent_status, kill_agent,
  update_scratch, send_file
- Script-based tool discovery: tools/ dir with --schema convention
- Feishu todo management script (tools/manage_todo)
- SQLite persistence: conversations, messages, config, scratch_area tables
- Sliding window context (100 msgs, slide 50, auto-summarize)
- Conversation summary generation via LLM on window slide
- Group chat support with independent session contexts
- Image understanding: multimodal vision input (base64 to API)
- Voice transcription via faster-whisper Docker service
- Configurable persona stored in DB
- diag command for session diagnostics
- System prompt restructured: persona + tool instructions separated
- RUST_BACKTRACE=1 in service, clippy in deploy pipeline
- .gitignore for config/state/db files

.gitignore

@@ -1,5 +1,5 @@
-/target
 config.yaml
-config.hera.yaml
+config.*.yaml
 state.json
-noc.service
+state.*.json
+*.db