refactor(intents): make hook ordering explicit and run hooks concurrently behind experimental.concurrent-hooks

[stefanhoelzl]

• Explicit ordering instead of registration order. Implicit dependencies between handlers on one hook point are now requires/provides capabilities or hook points:
  • delete shutdown: the agents require agent-stopped (CAPABILITY_AGENT_STOPPED), so they stop the agent only after the api-server has closed its terminal
  • delete/hibernate shutdown: the lifecycle claim provides workspace-claimed; the agent resolver and the api-server's terminal close require it
  • vscode:modal-changed: terminal-focus provides modal-recorded, which the agents require before re-reporting status
  • app:shutdown gains a handoff hook point between stop and quit for the update installer (quitAndInstall must start after teardown and before app.quit())
• Single-writer result folds. results[] carries no order: lastDefined becomes onlyDefined (throws when two handlers define a field), mergeRecords merges env/metadata maps with a per-key clash check, and the hand-written last-write-wins folds (resolve/open project, resolve workspace identity and state, get-status, switch, delete) use them. detect's blocking processes are concatenated.
• experimental.concurrent-hooks (default false, applies live): the dispatcher starts every handler whose requires are met at once and re-checks the waiting ones as each finishes; events take the same path. A hook point with a single handler keeps the sequential path, so its timing is unchanged. Sequential mode is tick-for-tick identical to before.
• e2e runs with the flag on (e2e/fixtures.ts), so an order-only dependency fails in e2e before the flag becomes the default. Locally: 5 repeats of the warm suite (600 spec runs) with the flag on, one failure — a pre-existing startup race (ch ws create right after ch project open, its nested project:open blocked by idempotency while app:ready restores the same project), being investigated separately.
• Docs: docs/INTENTS.md (ordering contract, fold policy, the flag, app-shutdown hook points), docs/TESTING.md, docs/USER_GUIDE.md (settings), CLAUDE.md.

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