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/draft_sync.py

@@ -0,0 +1,120 @@
+"""Mirror local drafts to the account's IMAP Drafts folder (SPEC §6.5 extension).
+
+Drafts are stored server-side as ``\\Draft`` messages so they can be continued on
+any standard mail client. IMAP messages are immutable, so each edit APPENDs a new
+copy and expunges the previous one (tracked by ``drafts.imap_uid``). Runs in the
+worker (credential decryption is worker-only, §10.2).
+"""
+
+from __future__ import annotations
+
+import contextlib
+import logging
+import uuid
+from typing import Any
+
+from sqlalchemy import select
+
+from app.db import session_scope
+from app.models import Account, Draft, Mailbox, Message
+from app.outbox.attachments import load_attachments
+from app.outbox.mime_build import build_mime
+from app.sync.provider_factory import build_provider
+
+logger = logging.getLogger(__name__)
+
+_DRAFT_FLAGS = frozenset({"\\Draft", "\\Seen"})
+
+
+async def _ensure_drafts_folder(provider: Any, account: Account, user_id: uuid.UUID) -> str:
+    """Return the account's Drafts folder path, creating one if it is missing."""
+    path = "Drafts"
+    await provider.create_mailbox(path)
+    remote = await provider.list_mailboxes()
+    uidvalidity = next((r.uidvalidity for r in remote if r.path == path), 0)
+    async with session_scope() as session:
+        existing = await session.scalar(
+            select(Mailbox).where(
+                Mailbox.account_id == account.id, Mailbox.special_use == "drafts"
+            )
+        )
+        if existing is not None:
+            return existing.path
+        session.add(
+            Mailbox(
+                account_id=account.id,
+                user_id=user_id,
+                path=path,
+                special_use="drafts",
+                uidvalidity=uidvalidity,
+            )
+        )
+    return path
+
+
+async def push_draft_to_imap_job(ctx: dict[str, Any], draft_id: str) -> None:
+    """APPEND the draft to the Drafts folder and expunge the previous copy."""
+    did = uuid.UUID(draft_id)
+    async with session_scope() as session:
+        draft = await session.get(Draft, did)
+        if draft is None:
+            return
+        account = await session.get(Account, draft.account_id)
+        if account is None:
+            return
+        user_id = draft.user_id
+        old_uid = draft.imap_uid
+        reply_to = (
+            await session.get(Message, draft.reply_to_message_id)
+            if draft.reply_to_message_id
+            else None
+        )
+        attachments = await load_attachments(session, user_id, draft)
+        _, sent_raw, _, _ = build_mime(account, draft, reply_to, attachments)
+        drafts_mb = await session.scalar(
+            select(Mailbox).where(
+                Mailbox.account_id == account.id, Mailbox.special_use == "drafts"
+            )
+        )
+        drafts_path = drafts_mb.path if drafts_mb else None
+        account_obj = account
+
+    provider = build_provider(account_obj)
+    new_uid = 0
+    try:
+        if drafts_path is None:
+            drafts_path = await _ensure_drafts_folder(provider, account_obj, user_id)
+        new_uid = await provider.append(drafts_path, sent_raw, _DRAFT_FLAGS)
+        if old_uid:
+            with contextlib.suppress(Exception):
+                await provider.delete_messages(drafts_path, [old_uid])
+    finally:
+        await provider.close()
+
+    if new_uid:
+        async with session_scope() as session:
+            draft = await session.get(Draft, did)
+            if draft is not None:
+                draft.imap_uid = new_uid
+
+
+async def remove_imap_draft_job(ctx: dict[str, Any], account_id: str, uid: int) -> None:
+    """Expunge a draft copy from the account's Drafts folder (on discard)."""
+    aid = uuid.UUID(account_id)
+    async with session_scope() as session:
+        account = await session.get(Account, aid)
+        if account is None:
+            return
+        drafts_mb = await session.scalar(
+            select(Mailbox).where(Mailbox.account_id == aid, Mailbox.special_use == "drafts")
+        )
+        drafts_path = drafts_mb.path if drafts_mb else None
+        account_obj = account
+    if drafts_path is None:
+        return
+    provider = build_provider(account_obj)
+    try:
+        with contextlib.suppress(Exception):
+            await provider.delete_messages(drafts_path, [int(uid)])
+    finally:
+        await provider.close()