ctrl: API routes for email surface (/ctrl/email)

[ssilvius]

API routes for the ctrl email surface. These expose the existing service layer as HTTP endpoints.

Routes:

• GET /mailboxes -- all mailboxes the user can access
• GET /threads?mailboxId=...&folderId=... -- threads in a folder
• GET /thread/:id -- thread with messages
• POST /compose -- send from any mailbox
• POST /reply -- reply to a thread
• GET /audiences -- newsletter audiences
• POST /campaign -- send a broadcast
• GET /classification/stats -- AI classification breakdown

Depends on: ctrl Phase 2 starting, platform providing the Hono API shell.
Uses: createMailServices(), createInboxEmailService(), existing service interfaces.