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/sync/supervisor.py

@@ -20,7 +20,7 @@ from sqlalchemy import select
 
 from app.db import session_scope
 from app.models import Account
-from app.sync.engine import live_loop
+from app.sync.engine import live_loop, secondary_poll_loop
 
 logger = logging.getLogger(__name__)
 
@@ -39,13 +39,29 @@ async def _run_account(account_id: uuid.UUID, stop: asyncio.Event) -> None:
                 await asyncio.wait_for(stop.wait(), timeout=_RECONNECT_BACKOFF)
 
 
+async def _run_secondary(account_id: uuid.UUID, stop: asyncio.Event) -> None:
+    while not stop.is_set():
+        try:
+            await secondary_poll_loop(account_id, stop)
+        except asyncio.CancelledError:
+            raise
+        except Exception:
+            logger.exception("secondary poll loop for %s crashed; retrying", account_id)
+            with contextlib.suppress(TimeoutError):
+                await asyncio.wait_for(stop.wait(), timeout=_RECONNECT_BACKOFF)
+
+
 async def start_supervisor(ctx: dict[str, Any]) -> None:
     """Launch a live loop per live account (called from the worker on_startup)."""
     async with session_scope() as session:
         account_ids = list(await session.scalars(select(Account.id).where(Account.state == "live")))
     stop = asyncio.Event()
     ctx["supervisor_stop"] = stop
-    ctx["supervisor_tasks"] = [asyncio.create_task(_run_account(aid, stop)) for aid in account_ids]
+    tasks: list[asyncio.Task[None]] = []
+    for aid in account_ids:
+        tasks.append(asyncio.create_task(_run_account(aid, stop)))  # INBOX IDLE
+        tasks.append(asyncio.create_task(_run_secondary(aid, stop)))  # other folders poll
+    ctx["supervisor_tasks"] = tasks
     logger.info("live supervisor started for %d account(s)", len(account_ids))