feat(api): GET /api/export/chat-html — 导出 1:1/群聊天为 HTML

支持 DM(talker_id) 与 群(room_id)，可选 start/end 时间范围；
is_send 决定气泡左右。对齐云客微信客户/群列表「导出HTML聊天记录」。

Co-Authored-By: Claude <noreply@anthropic.com>

yunke-server/app/api/main.py

@@ -17,6 +17,7 @@ Includes:
 * ``GET /api/sms`` (see :mod:`app.api.routers.sms`).
 * ``GET /api/sync/status`` (see :mod:`app.api.routers.sync`).
 * ``GET /api/search`` (see :mod:`app.api.routers.search`).
+* ``GET /api/export/chat-html`` (see :mod:`app.api.routers.export`).
 
 CORS is configured permissively (wildcard origin, no credentials) so the local
 frontend can call the API during development.
@@ -38,6 +39,7 @@ from app.api.auth import require_auth
 from app.api.routers import (
     calls,
     customer,
+    export,
     groups,
     media,
     messages,
@@ -65,6 +67,7 @@ app.include_router(calls.router)
 app.include_router(sms.router)
 app.include_router(sync.router)
 app.include_router(search.router)
+app.include_router(export.router)
 
 
 @app.get("/api/health")