Limit IoT MCP server to registry tools

[ShuxinLin]

Summary

• limit the IoT MCP server to registry discovery tools: sites, asset_ids, and assets
• add sites() using the registry-backed site discovery pattern from the pinned upstream IoT server
• make asset_ids() return only sorted assetnum values for a site
• make assets() return compact registry metadata, with optional assettype filtering
• improve MCP-visible docstrings using the FastMCP-style summary plus Args and successful-result Returns sections
• use backend-neutral registry database wording in IoT tool docs and tool errors
• remove _id, doctype, iot_asset_id, and wo_assetnum from src/couchdb/scenarios_data/shared/iot/asset_profile_sample.json
• update tests, docs, ToolUniverse/OpenCode examples, and legacy workflow messaging for the new IoT tool surface

Tool Surface

• sites() -> {"sites": [...]}
• asset_ids(site_name) -> bare asset id list for the site
• assets(site_name, assettype?) -> asset metadata rows: asset_id, description, assettype, vintage, n_sensors

Tests

• .venv/bin/python -m pytest src/servers/iot/tests src/mcphub/tests (13 passed, 5 skipped; registry integrations skipped locally)
• jq empty src/couchdb/scenarios_data/shared/iot/asset_profile_sample.json
• .venv/bin/python -m py_compile src/servers/iot/main.py src/servers/iot/tests/test_tools.py src/mcphub/workflows.py src/mcphub/tests/test_workflows.py
• MCP registry smoke check confirmed ['asset_ids', 'assets', 'sites']
• MCP docstring smoke check confirmed FastMCP-style summary, Args, and successful-result Returns sections for the IoT tools

[DhavalRepo18]

Once all the Tools are in place in the IoT, I will make a clean review.