feat(core): persist compaction model and provider state

[rekram1-node]

Issue for this PR

None.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Completed compaction messages and completion events now require model: Model.Ref and may carry providerState, using the same opaque state schema as assistants. State comes from the accepted summarization attempt and the route's provider-metadata namespace; rejected-attempt state is discarded.

Existing checkpoints and stored completion events get a best-effort model backfill from earlier model-bearing history, then later history, then the session model. unknown/unknown is the final fallback. Older exports remain importable and are normalized before storage; inferred models never acquire provider state. Existing database import paths are covered too.

Projection, clients, export/import, and sanitized exports preserve or redact the fields appropriately. Generated clients and existing fixtures are updated for the required field.

No changes to prompts, summary/recent content, retained history, or native-compaction execution/replay.

How did you verify your code works?

• 342 focused Core tests passed, including migration, retry-state isolation, projection replay, and transfer coverage.
• 146 Client tests and 139 focused TUI tests passed.
• All 3 new Schema tests passed. Full Schema suite: 58 passed, 1 pre-existing failure at test/contract-hygiene.test.ts:244 because unchanged src/integration.ts:62,68 uses Schema.Any.
• Core, Client, Schema, Protocol, Server, TUI, App, and website typechecks passed.
• Migration registry, generated documentation, and diff checks passed.
• Exercised the actual migration against a copied evaluation database in a rolled-back transaction: all 573 completed checkpoints received models, none needed the fallback. The copy and production database were left unchanged.

Screenshots / recordings

Not applicable; no UI behavior changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR