fix(device): create instances from installed templates

[xiami762]

Summary

• expose installed device templates through device_manage
• create device instances only after template discovery and tool-side installed-template validation
• reject undeclared or sensitive fields while allowing auth_state configuration
• simplify device integration skill guidance and keep page-specific JSON protocols out of the skill

Tests

• uv run pytest tests/tool/test_device_manage_tool.py tests/tool/test_device_plugin_index.py tests/tool/test_device_manage_prompt.py tests/server/routes/test_device_routes.py tests/skill/test_device_integration_guide_skill.py -q
• uv run ruff check flocks/tool/device/manage_tool.py tests/tool/test_device_manage_tool.py tests/skill/test_device_integration_guide_skill.py
• git diff --check