feat: recover missing conversations, fix media attachment, add manual inbox tab

Missing conversations: recipient Reddit accounts that are deleted or suspended
left conversations unaccounted for. A new RecipientAccountStatusService polls
Reddit for the users behind cached conversations and records their account
status durably, with progressive backfill and delta-media fixes in ChatService
so history and images are no longer dropped mid-sync.

Media: attachMedia now surfaces download failures as MediaAttachmentError so the
sync cursor can be retried instead of silently losing an image, recognizes image
bytes when Matrix returns a generic content type, and keeps separate gallery
occurrences when the same asset appears in more than one event.

Manual inbox tab: the conversations list now carries the reply-loop status, so
the inbox can separate conversations the operator is driving by hand from the
ones automation is still handling. A Manual filter pill and a per-row chip
explain why each conversation was handed over.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/frontend.md

@@ -63,6 +63,8 @@ Exchange-library uploads require an explicit consent checkbox before the raw ima
 
 Conversation reply composers include a collapsed saved-image picker. It lists only server-approved assets for the latest inbound request, keeps thumbnails blurred until revealed, and requires selection plus a dedicated confirmation dialog before sending. The server remains authoritative and may reject a choice if the conversation changes before the rate-limited send executes.
 
+The conversation inbox has a system-derived **Account deleted** bucket alongside the operator-maintained open, snoozed, and done queues. A deleted recipient is excluded from the default, unread, needs-reply, waiting, manual, and image buckets and is labelled in both the list and detail views. Suspended profiles are not treated as deleted.
+
 ## Feature structure
 
 Each route is a slice under `features/<name>/` with page/route components, local styles, and feature-specific helpers. Cross-feature visual/domain components live under `components/`; application lifecycle belongs under `app/`; transport belongs under `api/`.