refactor: remove pre-user compatibility paths

[KenTaniguchi-R]

Summary

• require current correlation, task, invite, card, and roster protocol fields
• remove mixed-version Durable Object defaults and local JSON passthrough behavior
• remove obsolete flat task-directory guard behavior and reserved line names
• retain migrations, malformed-row quarantine, and fail-closed security checks
• regenerate the protocol reference

Testing

• pnpm -r build
• pnpm -r typecheck
• pnpm -r test (1,356 passed; 5 intentional probes skipped)
• pnpm docs:check
• git diff --check

Closes #260

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