refactor: split monolithic main.py into services/ + ui/ modules (improve-maintainability)

- main.py: 4360 → 146 lines (96.6% reduction), entry layer only
- services/: rate_limiter, autostart, persona, connection, profile,
  hotspot, content, engagement, scheduler, queue_ops (10 business modules)
- ui/app.py: all Gradio UI code extracted into build_app(cfg, analytics)
- Fix: with gr.Blocks() indented inside build_app function
- Fix: cfg.all property (not get_all method)
- Fix: STATUS_LABELS, get_persona_keywords, fetch_proactive_notes imports
- Fix: queue_ops module-level set_publish_callback moved into configure()
- Fix: pub_queue.format_*() wrapped as queue_format_table/calendar helpers
- All 14 files syntax-verified, build_app() runtime-verified
- 58/58 tasks complete"

openspec/changes/improve-maintainability/specs/services-hotspot/spec.md

@@ -0,0 +1,12 @@
+## ADDED Requirements
+
+### Requirement: 热点探测函数迁移至独立模块
+系统 SHALL 将热点搜索与分析相关函数从 `main.py` 提取至 `services/hotspot.py`，包括：`search_hotspots`、`analyze_and_suggest`、`generate_from_hotspot`、`_set_cache`、`_get_cache`、`_fetch_and_cache`、`_pick_from_cache`、`fetch_proactive_notes`、`on_proactive_note_selected`。
+
+#### Scenario: 模块导入成功
+- **WHEN** `main.py` 执行 `from services.hotspot import search_hotspots, analyze_and_suggest` 等导入
+- **THEN** 所有函数可正常调用
+
+#### Scenario: 线程安全缓存随模块迁移
+- **WHEN** `_cache_lock`（`threading.RLock`）随函数一起迁移至 `services/hotspot.py`
+- **THEN** `_set_cache` / `_get_cache` 的线程安全行为保持不变