feat: add min-agent support

Summary

Registers min-agent so skills add installs skills where min-agent actually reads them.

min-agent (website) natively reads the Agent Skills locations .agents/skills/ (project) and ~/.agents/skills/ (global), exactly like Codex, Pi, fx, Warp, Zed etc. So this PR adds it as a universal agent — no agent-specific mirror directories, no duplicated symlinks.

Its own config home ~/.min-agent (overridable via MIN_AGENT_CONFIG_DIR) stores settings, sessions and the enabled-skill state file — never skills — so it is used for install detection only.

Changes

• src/agents.ts: new min-agent entry — universal .agents/skills paths, detected via the resolved config home (MIN_AGENT_CONFIG_DIR or ~/.min-agent), mirroring the GROK_HOME/SARVAM_HOME env-override pattern
• src/types.ts: min-agent AgentType union member
• src/use.ts: launch min-agent for skills use --agent min-agent
• README.md, docs/agents.md, package.json keywords: regenerated with scripts/sync-agents.ts
• tests/min-agent.test.ts: registry paths, universal classification, MIN_AGENT_CONFIG_DIR detection, --agent parsing

Verification

• node scripts/validate-agents.ts — all agents valid
• tsc --noEmit — clean
• vitest run tests/min-agent.test.ts — 5 passed
• prettier --check — clean
• Full suite: the only failures are the 6 pre-existing tests/invalid-local-lock.test.ts failures, identical on unmodified main (local-machine issue, same exposure noted in #2554); all other 1051 tests pass

Docs: min-agent reads skills from .agents/skills/ in the working directory and ~/.agents/skills/ globally; its config dir is MIN_AGENT_CONFIG_DIR ?? ~/.min-agent.