feat(cli): health --coach mode for first-week adoption walkthrough

[NagyVikt]

Summary

Adds `colony health --coach` — a first-week walkthrough that detects new vs returning repos and surfaces the NEXT habit to adopt. Step completion is event-observed, never user-clicked.

• Stage detection: `fresh` / `installed_no_signal` / `early` / `mid_adoption`
• 7-step ladder, each with `cmd:` and `tool:` strings:
  1. `install_runtime` — any IDE installed
  2. `first_task_post`
  3. `first_task_claim_file`
  4. `first_task_hand_off`
  5. `first_plan_claim` — closes the 0/47 gap
  6. `first_quota_release`
  7. `first_gain_review`
• New `coach_progress` SQLite table (migration 014, schema_version 13 → 14)
• New storage methods: `markCoachStep`, `listCoachSteps`, `firstObservationTs`, `countObservationsByKindSince`
• Shared `installed-ides` helper between `status` and `health-coach`
• `colony gain` emits a `coach_gain_review` observation so step 7 self-detects
• `--coach` mutex with `--fix-plan` (stderr warning, `--coach` wins), respects `--json`

Closes `⏳ Adoption coach mode in colony health that walks a new repo through first-week setup` under README §v0.x "Adoption nudges".

OpenSpec

`openspec/changes/health-coach-mode-2026-05-16/CHANGE.md`

Test plan

• `pnpm --filter colonyq typecheck` — clean
• `pnpm --filter colonyq test` — 293/293 pass (9 new health-coach tests)
• `pnpm --filter @colony/storage test` — 157/157 pass
• biome check on touched files — clean
• Manual smoke: fresh `COLONY_HOME`, `--json` payload, `--coach --fix-plan` mutex

Merge order

Touches `packages/storage/src/storage.ts`. Recommended last — both #575 (drift detector) and this PR extend `storage.ts` independently. Whichever lands second needs a trivial rebase.

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