Fix: conversation_artifacts missing for run_analysis_artifact

Summary

Resolved run_analysis_artifact failures caused by relation "conversation_artifacts" does not exist.

What changed

1. Applied the required database migration directly:
   • services/backend/src/db/migrations/0034_conversation_artifacts_analysis_workflow.sql
   • services/backend/src/db/migrations/0039_web_search_cache_knowledge_base.sql (kept schema in expected shape for related artifact/caching flows)
2. Added backend guardrails in services/backend/src/routes/bots/bots-chat-handlers.ts:
   • listConversationArtifacts(...) now catches PostgreSQL undefined_table (42P01) for conversation_artifacts and returns an empty list with a warning instead of crashing the chat flow.
   • loadCodeArtifact(...) now catches the same condition and throws an actionable error message instructing to run migration 0034_conversation_artifacts_analysis_workflow.sql.
   • Added isPgUndefinedTableError(...) helper to centralize this check.

Why

The runtime code expects conversation_artifacts to exist for loading/saving analysis artifacts. If a target Neon environment misses migration 0034, run_analysis_artifact fails with a raw SQL error. This change fixes current schema drift and improves resilience if drift reappears.

Validation

• Ran migration command path in project root and confirmed table exists.
• Verified relation:

SELECT to_regclass('public.conversation_artifacts');
-- conversation_artifacts

• Ran repository checks:
  • pnpm typecheck
  • pnpm lint

Both completed successfully with existing non-blocking warnings (no new errors introduced by this change).

Notes

• Full migration runner (pnpm migrate:neon) currently stops at an older non-idempotent migration (0007_exchange_credentials_and_orders.sql) in this environment due to relation "exchange_credentials" already exists.
• Applied targeted migrations to unblock the production issue immediately.