feat(chat): attachments, file viewers, and EA-style catchup

[harshithmullapudi]

Summary

• Chat attachments end-to-end — composer accepts uploads; the conversation view renders them via the new file-viewer registry. Office formats (docx/pptx via mammoth + a renamed office-viewer) and CSV (papaparse) join the image/PDF set; pptx-preview is dropped.
• Agent file access — new file-tools + file-resolver.server.ts let the agent read attachments. Gateway download splits into file-download.server.ts; signed-URL flow (file-signed-url.server.ts + the two new fs.signed routes) gives agent and viewers short-lived access without leaking PATs.
• EA-style catchup — voice summariser prompt rewritten from butler-inventory to chief-of-staff (leads with what's blocking, groups by next decision, makes one soft recommendation, drops the "sir"). Quick Chat is now scoped per local-day (mirrors WhatsApp daily-conversation pattern in message-processor.ts:62), and every /api/v1/inbox/summarise appends the spoken summary to that day's Quick Chat as an Agent turn so it's scrollable.

Test plan

• Upload a docx, pptx, csv, image, and pdf from the chat composer — each renders inline via the appropriate viewer.
• Agent can read an attached file via the file-tools and reason about its contents in the reply.
• Gateway signed-URL: viewers and agent can fetch attachments without a PAT; URL expires.
• Press the inbox pill catchup with mixed items (PR, calendar event, email) — spoken summary opens with what matters now, not a category inventory; no "sir"; includes a recommendation where obvious.
• First catchup of the day creates a fresh Quick Chat; subsequent catchups on the same day append to it; the next calendar day starts a new Quick Chat.
• Open Quick Chat in the web UI — the catchup appears as an Agent message, scrollable.

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