Centralize persisted state

[ctoth]

Summary

• add one shared persistence owner for versioned local storage, migration, quota/error handling, and IndexedDB opening/upgrades
• migrate preferences, channel history, command history, output history, auth tokens, checkpoints, session logs, file transfers, and autolog storage to that owner
• preserve legacy raw and versioned data through schema migration, including the existing raw auth token and output-log shapes

Root cause

Persisted state was owned independently by each feature. The stores used incompatible payload shapes, version handling, error behavior, and IndexedDB upgrade paths, so blocked storage or future schema changes had to be solved repeatedly in each caller.

Impact

All current durable client state now goes through the same versioned contract. Blocked or full local storage is handled without crashing consumers, legacy values migrate into the shared envelope, and IndexedDB creation/upgrades use one entry point.

TDD and validation

• observed the new persistence suite fail before src/persistence.ts existed
• observed the legacy raw-token regression fail before raw-string migration was added
• npm test — 107 files, 1,063 tests passed
• npm run typecheck
• npm run lint:staged
• git diff --cached --check

Closes #76