Add Grok Build to midas init

[vornicx]

Summary

Add Grok Build as a first-class midas init client using Grok's native MCP CLI and TOML schema.

Behavior

• midas init detects the grok executable and runs:
  grok mcp add --scope user midas -e MIDAS_MCP_EMBEDDER=local -e MIDAS_MCP_CLIENT=grok-build -- midas-mcp
• --project-scoped also supplies MIDAS_MCP_NAMESPACE=auto.
• midas init --dry-run [--json] reports the exact Grok command without writing.
• midas status --json reads ~/.grok/config.toml / [mcp_servers.midas] and reports command, client ID, and namespace.
• midas doctor includes Grok Build in wired-client detection.
• midas uninstall uses grok mcp remove --scope user midas.
• README, llms.txt, and changelog now document Grok Build.

Verification

• uv run pytest -q → 349 passed, 2 skipped
• uv run pytest tests/test_cli.py -q → 24 passed
• git diff --check
• python3 -m compileall -q midas tests
• Live compatibility check with Grok Build CLI 0.2.106 in an isolated temporary HOME:
  • native grok mcp add generated [mcp_servers.midas] with all expected MIDAS_* values
  • grok mcp list --json and grok inspect --json discovered the server
  • midas status --json reported Grok Build, client_id=grok-build, and project scope
  • native grok mcp remove removed it cleanly