feat: add agentty agent support to the install CLI

[davidwed]

What does this PR do?

Add automatic detection, skill installation, MCP registration, uninstall, and --clients selection for the agentty coding agent (https://github.com/1ay1/agentty), following the established detected-agent pattern (OpenHands template):

• Detection: ~/.agentty/ directory or agentty CLI on PATH; new cbm_detected_agents_t.agentty field probed in cbm_detect_agents()
• Selection: --clients=agentty token via the CLI_CLIENTS table
• Install: codebase-memory skill to ~/.agentty/skills/ (Claude-compatible SKILL.md; user scope = trusted on load) and MCP server entry in ~/.agentty/mcp.json (standard mcpServers shape via the existing cbm_install_editor_mcp adapter). Instructions/hooks/tiered profiles deliberately withheld — agentty documents no AGENTS.md equivalent.
• Uninstall: owned-document matching counterpart; user-modified files and foreign servers survive; skill dir removed only when empty
• Docs: README agent table row, pkg/npm/README.md (40 detected), docs/llms.txt + docs/index.html + badge (46 surfaces / 40 detected), contract test cli_supported_agent_surfaces_match_installers and the --help enumeration aligned to 46/40 in lockstep

Tests: detection, --clients vocabulary + leak guard, install plan and schema checks, and an install/uninstall roundtrip asserting foreign-server and user-skill preservation in both directions.

Checklist

• Every commit is signed off (git commit -s) — required, CI rejects
  unsigned commits (DCO, see CONTRIBUTING.md)
• Tests pass locally (make -f Makefile.cbm test)
• Lint passes (make -f Makefile.cbm lint-ci)
• New behavior is covered by a test (reproduce-first for bug fixes)

[github-actions]

Thanks for opening this — it has been seen, and it is queued.

This note is automated, but it is not a brush-off: it exists so you know where your PR stands instead of having to guess from silence.

Current review status: working through a backlog. 0.9.1-rc.1 is out, so the release freeze that held reviews is over — but it left a large queue of open pull requests behind it, and we are reading through them oldest-first. The background is in discussion #1144.

What that means for this PR, concretely:

• It will not be closed for inactivity. No stale bot touches pull requests here.
• It may still sit a while before a human reads it. That is on us, not on you.
• Older PRs are read first, so a recent one is not being skipped — it is behind a queue.

Things that will genuinely speed it up whenever review does happen:

• Keep it rebased on main — the tree is moving quickly right now, and a conflicting branch cannot be reviewed as the diff you intended.
• Get CI green, or say which failures you believe are pre-existing.
• Keep the change to one claim. Bundled features and refactors get split before they get merged, which costs you a round trip.
• Every commit needs a sign-off (git commit -s) — CI enforces DCO.

If this fixes a bug, a reproduction we can run is worth more than a description of the symptom.

Thanks for contributing, and sorry in advance for the wait.

[DeusData]

Thank you, @davidwed! This is a clean, well-tested addition:

• The paths match agentty's own docs (~/.agentty/mcp.json at user scope, ~/.agentty/skills/).
• Uninstall removes only what we own.
• Every headline count and the contract test stay in lockstep.

We'd like agentty in, with two changes before merge:

1. Please register agentty in the table-driven client registry (src/cli/agent_clients.c) instead of the legacy detector.

   • Every client added since Grok Build lives there: Qoder, Kimi Code, GitLab Duo, Rovo Dev, Amp, Devin, Tabnine, CodeBuddy, IBM Bob Shell, Pochi, Pi and Oh My Pi. Each entry carries its stability class, capability bits, detection command and install/remove callbacks.
   • The legacy path is cbm_detected_agents_t, CLI_CLIENTS, the plan-names table and the hand-written install/uninstall blocks. We are no longer extending it.
   • Moving agentty to the registry also gives you detection output, --clients, --plan and uninstall from that one entry.
   • On the current legacy path, print_detected_agents doesn't list agentty. A machine with only agentty would print "Detected agents: (none)" and then install anyway.

2. Honor $AGENTTY_MCP_CONFIG.

   • agentty's plugin docs say this variable points at an explicit file that overrides both the user and the project mcp.json.
   • When it is set, agentty never reads the entry in ~/.agentty/mcp.json, yet install still reports success.
   • Writing to the override file when the variable is set, as we already do for CLAUDE_CONFIG_DIR, GROK_HOME and VIBE_HOME, closes that gap.

One small thing: the suite comment in tests/test_cli.c changes "6 tests" to "7 tests", but the group already has more than that, so it's fine to drop the count.

Thanks again for picking this up and for modelling it so carefully on the existing clients!