Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

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

backend/app/sync/folder_names.py

@@ -0,0 +1,48 @@
+"""Special-use inference from folder names (SPEC §6.3 fallback heuristics).
+
+Used only when the server does not advertise SPECIAL-USE. Includes Polish names
+(Wysłane, Kosz, ...) alongside English/German, per the spec's i18n intent.
+"""
+
+from __future__ import annotations
+
+_NAME_MAP: dict[str, str] = {
+    # sent
+    "sent": "sent",
+    "sent items": "sent",
+    "sent mail": "sent",
+    "wysłane": "sent",
+    "wyslane": "sent",
+    "elementy wysłane": "sent",
+    "gesendet": "sent",
+    # drafts
+    "drafts": "drafts",
+    "draft": "drafts",
+    "robocze": "drafts",
+    "kopie robocze": "drafts",
+    "entwürfe": "drafts",
+    # trash
+    "trash": "trash",
+    "deleted": "trash",
+    "deleted items": "trash",
+    "kosz": "trash",
+    "papierkorb": "trash",
+    # junk
+    "junk": "junk",
+    "spam": "junk",
+    "bulk mail": "junk",
+    "wiadomości-śmieci": "junk",
+    # archive
+    "archive": "archive",
+    "archiwum": "archive",
+    "all mail": "archive",
+    "archiv": "archive",
+}
+
+
+def infer_special_use(path: str) -> str | None:
+    """Infer a special_use value from a mailbox path/name (case-insensitive)."""
+    if path.upper() == "INBOX":
+        return "inbox"
+    leaf = path.replace("\\", "/").split("/")[-1].strip().lower()
+    return _NAME_MAP.get(leaf) or _NAME_MAP.get(path.strip().lower())