Track powerio 0.3.3 tool rename; OpenDSS distribution on-ramp

[samtalki]

Summary

• Pins PowerMCP to powerio[mcp,matrix] >= 0.3.3.
• Re-exports the canonical PowerIO MCP server instead of keeping a local tool copy.
• Exposes exactly the PowerIO tool surface: convert, save, summary, parse, normalize, matrix, and display.
• Removes the local read_display_file overlay because display now comes from PowerIO.
• Removes the OpenDSS compile_distribution wrapper; OpenDSS now compiles DSS files emitted by PowerIO.
• Documents the intended distribution flow: save(to_format="dss", json=..., json_format="bmopf-json"), then compile_opendss_file(...).
• Updates bridge docs and tests to use parse, save, matrix, the canonical summary shape, and stable schema markers.

Validation

• .venv/bin/python -m py_compile powerio/powerio_mcp.py tests/test_powerio_server.py pandapower/panda_mcp.py PyPSA/pypsa_mcp.py Egret/egret_mcp.py ANDES/andes_mcp.py OpenDSS/opendss_tools/configuration.py
• .venv/bin/python -m pytest tests/test_powerio_server.py -q
• .venv/bin/python -m pytest tests/ -q
• git diff --check origin/main...HEAD

[samtalki]

@qian-harvard this is ready for review (can't request reviews for some reason).

This PR completes the integration of PowerMCP with PowerIO's canonical MCP server for file IO. The exposed PowerIO tool surface is now 7 tools:

convert, save, summary, parse, normalize, matrix, display

Distribution systems now flow through PowerIO as BMOPF JSON transport, then write DSS only when the OpenDSS runtime needs a file:

save(to_format="dss", json=..., json_format="bmopf-json") -> compile_opendss_file(...)

Decisions to be made

• The companion PowerIO PR MCP: distribution + display tools; unified tool surface eigenergy/powerio#141 now adds stable payload markers such as schema, schema_version, domain, model, json_format, source_format, and warnings. This PR tests those markers for parse, summary, matrix, and display. Please make sure you are happy with the payload markers and the test.
• Naming for output functions: save currently means "write a canonical JSON transport or source case to a target format/path." If you strongly prefer write, we should change it before merge; I do not think we should expose both.