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/models.py

@@ -10,6 +10,7 @@ import datetime as dt
 import uuid
 
 from sqlalchemy import (
+    BigInteger,
     ForeignKey,
     Index,
     Integer,
@@ -54,6 +55,11 @@ class User(Base):
     settings: Mapped[dict[str, object]] = mapped_column(
         JSONB, nullable=False, server_default=text("'{}'")
     )
+    # Storage quota in bytes; per-user so an admin can override it later.
+    # Default 5 GiB (5 * 1024^3).
+    quota_bytes: Mapped[int] = mapped_column(
+        BigInteger, nullable=False, server_default=text("5368709120")
+    )
     created_at: Mapped[dt.datetime] = _now()
 
 
@@ -68,6 +74,8 @@ class Account(Base):
     email: Mapped[str] = mapped_column(CITEXT, nullable=False)
     display_name: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
     color: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("'#888888'"))
+    # Per-account HTML signature, inserted into new messages (and via compose menu).
+    signature: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
     imap_config: Mapped[dict[str, object]] = mapped_column(JSONB, nullable=False)
     smtp_config: Mapped[dict[str, object]] = mapped_column(JSONB, nullable=False)
     secret_ct: Mapped[bytes] = mapped_column(BYTEA, nullable=False)
@@ -158,6 +166,9 @@ class Message(Base):
     cc_addr: Mapped[list[dict[str, str]]] = mapped_column(
         JSONB, nullable=False, server_default=text("'[]'")
     )
+    bcc_addr: Mapped[list[dict[str, str]]] = mapped_column(
+        JSONB, nullable=False, server_default=text("'[]'")
+    )
     date_hdr: Mapped[dt.datetime | None] = mapped_column(TIMESTAMP(timezone=True))
     internal_date: Mapped[dt.datetime] = mapped_column(TIMESTAMP(timezone=True), nullable=False)
     flags: Mapped[list[str]] = mapped_column(
@@ -233,6 +244,9 @@ class Draft(Base):
     )
     kind: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("'reply'"))
     payload: Mapped[dict[str, object]] = mapped_column(JSONB, nullable=False)
+    # UID of the mirrored copy in the account's IMAP Drafts folder (so the draft
+    # is visible/continuable on other mail clients). Replaced on each edit.
+    imap_uid: Mapped[int | None] = mapped_column(Integer)
     updated_at: Mapped[dt.datetime] = _now()