refactor: remove legacy migration and reconciliation paths

[iamjr15]

Summary

• Collapse all historical SQL into one production-verified current-schema baseline.
• Remove obsolete migration phases, Durable Object reconciliation, and sandbox workspace/snapshot transition paths.
• Keep the three required workflows and make static checks run on both PRs and main pushes.

Architecture

The production database, Drizzle journal, and source schema now share one exact baseline. Runtime Durable Objects fail closed on schema mismatch instead of carrying release-time compatibility migrations. Daytona sandboxes use only the configured snapshot and workspace identity.

Decisions

• Keep only 0000_current_schema.sql; Git retains historical migration history.
• Reconcile the production Drizzle ledger atomically to that baseline.
• Keep static checks, snapshot publication, and audit archival because each owns a distinct production responsibility.
• Remove migration exceptions, raw phases, snapshot upgrades, workspace transitions, and DO reconciliation endpoints.

Verification

• pnpm db:migrate -- --dry-run
• pnpm db:generate
• pnpm typecheck (clean forced rebuild)
• pnpm lint
• pnpm build
• pnpm architecture:check
• pnpm deadcode
• actionlint on all workflows
• git diff --check