Two-way draft sync, signatures, sent/bcc fixes, and mail-list UI

Backend
- Sent copies: persist locally on send + periodic multi-folder CONDSTORE poll
  (Sent/Archive/Trash/Junk) so they thread and show without an IDLE-only INBOX.
- Bcc: transmitted copy omits Bcc, Sent copy keeps it; store/display bcc_addr.
- Drafts: mirror local drafts to the IMAP Drafts folder (append/replace/expunge);
  inbound sync of foreign drafts (un-threaded) with adopt-to-edit + dedup by UID.
- Per-user storage quota (5 GiB default) and manual "sync all folders" action.
- Account editing (display/color/server/password) and per-account HTML signature.
- Account view scoped to that account's inbox; new migrations 0006–0009.

Frontend
- Mail-list pagination, folder filters (All/Unread/Pinned), sort toggle, refresh.
- Aligned + widened mail-list margins; reading-pane bars fixed height.
- Rich-text composer: color palette, highlight, image; attachments; expand/pop-out.
- Signatures: auto-insert for new mail, replace on From change, reply insert.
- Restore/Delete actions per folder; drafts view merges local + remote, date-sorted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/outbox/attachments.py

@@ -0,0 +1,40 @@
+"""Resolve a draft's compose-attachment ids into raw (filename, mime, data) tuples."""
+
+from __future__ import annotations
+
+import uuid
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.indexer import blobstore
+from app.models import ComposeAttachment, Draft
+
+
+async def load_attachments(
+    session: AsyncSession, user_id: uuid.UUID, draft: Draft
+) -> list[tuple[str, str, bytes]]:
+    """Return each of the draft's compose attachments as ``(filename, mime, data)``."""
+    raw_ids = draft.payload.get("attachment_ids") or []
+    if not isinstance(raw_ids, list) or not raw_ids:
+        return []
+    ids: list[uuid.UUID] = []
+    for value in raw_ids:
+        try:
+            ids.append(uuid.UUID(str(value)))
+        except ValueError:
+            continue
+    if not ids:
+        return []
+    rows = await session.scalars(
+        select(ComposeAttachment).where(
+            ComposeAttachment.id.in_(ids), ComposeAttachment.user_id == user_id
+        )
+    )
+    by_id = {r.id: r for r in rows}
+    out: list[tuple[str, str, bytes]] = []
+    for i in ids:
+        att = by_id.get(i)
+        if att is not None:
+            out.append((att.filename, att.mime_type, blobstore.load(user_id, att.blob_sha256)))
+    return out