fix: complete remaining 8 optimization items

- HTTP connection pooling: UpstreamClient & WebsiteClient reuse httpx.Client
- Deduplicate decimal_string into shared app/utils/number.py
- Split scheduler transaction: snapshot write → webhook/website sync in separate sessions
- Remove hardcoded 170.106.100.210 migration from database.py
- Reset consecutive_failures on upstream update
- Healthcheck: install curl, replace python -c with curl -f
- Add .dockerignore to reduce build context
- Frontend: add axios-retry with exponential backoff (5xx/network errors only)

backend/app/database.py

@@ -64,15 +64,4 @@ def _migrate_custom_pages():
                     "AND NULLIF(TRIM(login_password), '') IS NOT NULL"
                 )
             )
-        conn.execute(
-            text(
-                "UPDATE custom_pages "
-                "SET access_mode = 'remote_browser', use_proxy = 0 "
-                "WHERE url LIKE :host OR url LIKE :host_slash OR url LIKE :host_port"
-            ),
-            {
-                "host": "%://170.106.100.210",
-                "host_slash": "%://170.106.100.210/%",
-                "host_port": "%://170.106.100.210:%",
-            },
-        )
+