[pyproject] Clean up stale uv.workspace member paths

The `[tool.uv.workspace]` members list in root `pyproject.toml` references paths that don't match the actual directory layout:

\`\`\`toml
members = [
\"labs/module4/notebooks/mcp\", # does not exist
\"labs/module4/mcp_server/weather_server\", # does not exist
\"labs/module4/notebooks/common/mcp_server/weather_server\" # does not exist
]
\`\`\`

The only MCP server \`pyproject.toml\` in the repo lives at \`labs/module4/notebooks/mcp_servers/weather_server/pyproject.toml\`.

\`uv sync\` may be silently ignoring these missing entries (or warning on them), which makes the workspace definition misleading for new contributors.

### Suggested fix
Replace the three stale paths with the single correct one:

\`\`\`toml
[tool.uv.workspace]
members = [\"labs/module4/notebooks/mcp_servers/weather_server\"]
\`\`\`

…or remove them entirely if the weather server is intended to be standalone.

### Context
Discovered while planning a restructure that adds \`labs/\` as a new workspace member (to host a shared \`labs_common\` package for model-ID config). Flagging separately so that cleanup can be scoped on its own.