refactor: package code organization waves 6–7 (#2166)
## Summary
Waves 6–7 of package code organization (plan:
`docs/plans/2026-07-14-001-refactor-package-code-organization-plan.md`),
after #2148.
### Wave 6
| New module | Parent |
|---|---|
| `merger-autostash-labels.ts` | `merger.ts` |
| `types/agent-state.ts` | `types.ts` |
| `app/api/tasks-lifecycle.ts` | `legacy.ts` |
| `task-store/task-row-mappers.ts` | `remaining-ops-3.ts` (rename) |
### Wave 7
| New module | Parent |
|---|---|
| `self-healing-optional-step-revision.ts` | `self-healing.ts` |
| `self-healing-path-utils.ts` | `self-healing.ts` |
| `merger-git-parse` (+ `quoteArg`, `getBranchChangedFiles`) |
`merger.ts` |
| `app/api/settings.ts` | `legacy.ts` |
Public import paths stay stable via re-exports.
## Test plan
- [x] engine + dashboard typecheck (incl. app)
- [x] eslint on touched modules
- [x] merger-autostash / parse-porcelain / getBranchChanged / api-tasks
- [ ] CI merge gate
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added a dedicated task lifecycle API client (task promotion, merge,
retry/reset/duplicate, pause/unpause, archive/unarchive, revert, plan
approve/reject) plus branch-group and planner oversight actions.
* Added a settings/config API service (effective task settings, update
check/refresh/install).
* Introduced standardized agent lifecycle states with identity/ephemeral
detection helpers.
* **Bug Fixes**
* Improved autostash label compatibility and NUL-delimited changed-file
detection for branch diffs.
* **Refactor**
* Modularized merger labeling/parsing, self-healing helpers, and
lifecycle/type wiring while keeping behavior consistent.
* **Tests**
* Updated merger verification tests for `git diff -z` output handling.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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