feat(agent-manager): add Antigravity CLI adapter

[nnhhoang]

Summary

Adds an antigravity_cli agent adapter so ai-devkit can detect, list, and inspect Google's Antigravity CLI (agy) alongside Claude, Codex, Gemini, and Grok. This is the runtime/agent side of Antigravity and is independent of the existing antigravity environment (which configures the Antigravity IDE), the same way gemini_cli is independent of the gemini environment.

How it works

• Detects agy processes from the shared AgentDetectionContext snapshot (processNames = ['agy']), falling back to captureProcessSnapshot for standalone use.
• Resolves each live process to its conversation through ~/.gemini/antigravity-cli/cache/last_conversations.json, a { "<cwd>": "<conversationId>" } map the CLI keeps per workspace (ANTIGRAVITY_CLI_HOME overrides the base).
• Lists history from brain/ instead. That cache holds only the current conversation of each workspace, so listing from it would hide every older conversation of a cwd; brain/ is the complete set. The cache is then used for what it is — the cwd of a workspace's current conversation.
• Reads the transcript from brain/<conversationId>/.system_generated/logs/transcript.jsonl: user prompts are the text inside <USER_REQUEST>...</USER_REQUEST> of type: "USER_INPUT" records, assistant turns are type: "PLANNER_RESPONSE", tool calls and SYSTEM records are skipped unless verbose. Summary is the last user request; last activity is the newest record created_at.

Known limitation: cwd for older conversations

Antigravity records a conversation's workspace nowhere except that cache — transcript.jsonl and transcript_full.jsonl contain no cwd, and conversations/<id>.db keeps its metadata in protobuf blobs (trajectory_metadata_blob, steps.metadata) with no readable path column. A conversation the cache no longer names is therefore listed with cwd: '' and surfaces under agent sessions --all rather than a cwd-scoped listing. Listing it without a cwd beats hiding it.

Changes

• New AntigravityCliAdapter (self-contained, inline parsing like the other recent adapters) + unit tests.
• AgentType/StartableAgentType gain antigravity_cli; AGENTS.antigravity_cli = { command: 'agy', matches: matchArgv0('agy') }; exported from the package.
• Wired into the agent command and channel runner; TYPE_LABELS, --type help, and VALID_AGENT_TYPES updated.
• README matrix gains an Antigravity CLI row (yes | yes) instead of ticking the Antigravity IDE row: remote control drives agy, not the IDE, and Setup is already true since the antigravity-cli environment shipped in feat(cli): add Antigravity CLI environment #134. Same separation the web docs already use.
• dev-lifecycle docs under docs/ai/*/feature-antigravity-cli-adapter.md.

Testing

• npx nx run agent-manager:test (594) and npx nx run cli:test (1057) pass; husky pre-commit ran all packages.
• Verified against real agy data on disk: listSessions() returns all 5 conversations under brain/ where the cache named 1, and listSessions({ cwd }) still returns exactly the one belonging to that workspace.
• detectAgents() with a live agy process resolves the cwd via last_conversations.json to its conversation and summary.

[codeaholicguy]

The implementation does not fully satisfy the stated requirement for historical Antigravity CLI sessions. listSessions() only reads cache/last_conversations.json, which is documented as the current conversation per cwd, so older brain/ transcripts can be missed.

[nnhhoang]

Sorry for the long silence on this one. Rebased onto main and fixed the review comment: listSessions() now walks brain/ instead of last_conversations.json, so older conversations aren't hidden anymore — on my machine it went from 1 session to all 5. CI is green, ready for another look.