feat: add Intercom integration

[Empreiteiro]

Summary

• Add Intercom as a new data source with 8 tables: contacts, companies, conversations, conversation_parts, tags, teams, admins, articles
• Include 5 report templates: Support Overview, Response Time, Team Performance, Customer Health, Knowledge Base
• Backend: ask_intercom.py (fetches Intercom API, loads into SQLite, LLM + SQL Q&A), intercom_router.py (test-connection, discover, refresh-metadata)
• Frontend: IntercomSourceForm.tsx with access token input, connection test, and resource discovery

Test plan

• Enter a valid Intercom access token and verify test connection succeeds
• Verify resource discovery lists all 8 Intercom tables with record counts
• Connect the source and verify metadata refresh populates table_infos
• Ask a natural language question and verify SQL is generated and executed against Intercom data
• Verify i18n strings render correctly in EN, PT, and ES
• Run npm run typecheck (passes)

Closes #69

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