feat(github): add PR comment cutover command + cutover fixes

[aparajon]

Summary

Add cutover via PR comment command, sentinel-based crash recovery, and cutover state fixes.

Cutover via PR comment — new `schemabot cutover -e ` command. Validates apply state, resolves tern client via stored deployment, triggers cutover, posts acknowledgment comment. Error handling for missing apply ID, missing environment, and environment-based instance routing.

Sentinel-based crash recovery — when a container restarts while a task is in `waiting_for_cutover`, check whether Spirit's `_spirit_sentinel` table exists in the target database. If it does, transition to a new `recovering` state that blocks cutover until Spirit re-reaches `WaitingOnSentinelTable` from its checkpoint. Replaces the previous blanket `CanEngineOverrideTaskState` guard with evidence-based recovery. Future: block/spirit#844 will add a `resume` field to replace the sentinel check.

ReadyToComplete centralized — set in `transitionTaskState` so both atomic and sequential modes mark tasks ready when entering `waiting_for_cutover`.

Engine state normalization — `NormalizeTaskStatus` converts camelCase Spirit states to canonical snake_case. Fixes CLI and PR comment rendering.

State downgrade prevention — Progress API only overwrites task state when the task is still pending or running, using sentinel-aware reconciliation.

Cutover UX — yellow progress bars and `⏸️ Ready for cutover` (green reserved for completions). Cutover footer includes apply ID and environment. Recovering state shows `🔄 Recovering...` with last known progress bar.

Templates — all cutover PR comments rendered via `pkg/webhook/templates/cutover.go`. AGENTS.md guideline: all PR comments must use templates.

Documentation — new `docs/cutover.md` covering the cutover lifecycle, sentinel table mechanism, Spirit's rename-under-lock algorithm, force-kill behavior, and recovery state. Updated `pkg/state/README.md` with recovering state.

[Copilot]

Pull request overview

This PR fixes progress/cutover state reporting across the Progress API and PR comment rendering, ensuring engine-reported states (including Spirit camelCase) are normalized to canonical task states and that tasks in waiting_for_cutover are counted as ready for cutover.

Changes:

• Prevent Progress polling from overwriting storage states beyond pending/running (avoids downgrades after restart when the engine reports pending/no active migration).
• Add ready_to_complete to TableProgress (proto + server population) and set ReadyToComplete when tasks enter waiting_for_cutover (atomic path).
• Normalize per-table engine progress states via state.NormalizeTaskStatus instead of strings.ToUpper.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkg/tern/local_client.go	Adjusts Progress polling state update rules; normalizes engine per-table states; returns ReadyToComplete in TableProgress.
pkg/tern/local_client_integration_test.go	Adds an integration test intended to validate Progress state normalization and ReadyToComplete behavior.
pkg/tern/local_apply.go	Sets Task.ReadyToComplete when atomic progress transitions to waiting_for_cutover.
pkg/proto/ternv1/tern.pb.go	Regenerated Go proto to include TableProgress.ready_to_complete.
pkg/proto/tern.proto	Adds ready_to_complete field to TableProgress message.

Files not reviewed (1)

• pkg/proto/ternv1/tern.pb.go: Language not supported

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