Remove task shares

[mrubens]

Summary

• remove the unused task_shares table and Drizzle relation from the live schema
• remove the TaskShare / CreateTaskShare types and server exports
• add a generated migration that drops task_shares from existing databases

Validation

• migrated a fresh disposable Postgres database and verified public.task_shares does not exist
• pnpm --filter @roomote/db check-types
• pnpm --filter @roomote/db lint
• DB tests: 218 passed
• pnpm lint:fast
• pnpm check-types:fast
• pnpm knip

[roomote-roomote]

No code issues found. See task

Reviewed the removal of the task_shares table, its Drizzle relation, the TaskShare/CreateTaskShare types, the server exports, and the 0002_remove_task_shares migration. The migration chain is consistent (0002 snapshot prevId matches the 0001 snapshot id, journal appended correctly, and the new snapshot no longer contains task_shares), no application code references the removed symbols, and pnpm --filter @roomote/db check-types passes.