feat: Verify migration rollback contracts against current schema

[Devadakene]

Closes #1192

Description

Closes #

This PR implements verification of migration rollback contracts and ensures deterministic checking of boundaries without destructive transformation. It updates the initial application startup logic to validate the state of the schema deterministically.

Key Changes

• Migration Application (src/migrate.ts):

  • Extracted the main migration logic into a reusable applyMigrations function.
  • Added a new validateSchemaState function that ensures the app database does not have unapplied schema drifts or unexecuted migrations relative to the .sql files.

• Initialization Logic (src/db/index.ts):

  • Replaced the hardcoded, single-migration script approach with a deterministic check utilizing applyMigrations() and validateSchemaState().
  • On application startup (initializeDb), it will now deterministically apply or validate the expected layout, fulfilling the fresh-install and upgrade-paths criteria.

• Automated Rolling Verification (src/migrations.test.ts):

  • Implemented a complete verification suite (Migration Rollback Contracts) using an in-memory db.
  • Runs every discovered migration UP, then runs DOWN (if the rollback script is present), and verifies that the sqlite_master metadata reverts identically to the pre-migration state.
  • Finally, replays the UP migration to proceed up the sequence, ensuring ordering, compatibility, and rollback boundaries are correct and strictly valid for the codebase.

Verification Checklist

• Implementation matches issue description
• All tests created and passing
• Fresh-install and upgrade paths validate expected schema/state before application work proceeds
• Ordering, compatibility, rollback boundaries, and destructive changes are checked deterministically
• Existing deployed data remains readable without implicit destructive transformation

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