fix(device): per-device tool enable/disable isolation

[duguwanglong]

Root cause: tool_settings in flocks.json was keyed globally by tool name, so toggling a tool for Device A silently affected Device B when both shared the same storage_key (same product version, different instance names).

Solution: introduce a dedicated device_tool_settings SQLite table that stores per-device tool overrides independently of the shared global overlay.

Schema:
PRIMARY KEY (device_id, tool_name)
FOREIGN KEY device_id REFERENCES device_integrations(id) ON DELETE CASCADE

Changes:

• models.py: register DDL via Storage.register_ddl(); CASCADE handles cleanup automatically when a device row is deleted
• store.py: add get/set/delete/list/list_all async CRUD; set and delete bump _device_revision() so the session runner's system-prompt cache invalidates
• registry.py: ToolRegistry.execute() checks per-device DB override before activating credentials; gate is in try/except so a DB hiccup never blocks a tool that is globally enabled
• routes/tool.py: PATCH /api/tools/{name}?device_id= routes per-device toggles to the new DB table instead of flocks.json
• routes/device.py: GET /api/devices/{id}/tools and PATCH /api/devices/{id}/tools/{name} endpoints; DELETE /api/devices/{id} no longer needs manual cleanup (ON DELETE CASCADE)
• prompt.py: build_device_context_section() loads all per-device overrides in one SQL query (list_all_device_tool_settings) instead of N+1 calls; disabled tools are annotated with device name and device_id so the Agent knows not to attempt calling them
• webui: DeviceIntegration page loads per-device enabled state from GET /api/devices/{id}/tools and routes toggle to PATCH /api/devices/{id}/tools/{name}; wizard mode hides the tool tab entirely (no device_id exists yet, so a per-device toggle is impossible)
• tests: 52 passing (18 new); covers CRUD, CASCADE delete, cache-revision bumping, batch query correctness, Agent prompt display accuracy

Fixes: toggling a tool for one device no longer affects other devices of the same product version.