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/tests/sync/test_folder_names.py

@@ -0,0 +1,34 @@
+"""Folder-name special-use heuristics (SPEC §6.3)."""
+
+from __future__ import annotations
+
+import pytest
+
+from app.sync.folder_names import infer_special_use
+
+
+@pytest.mark.parametrize(
+    "path,expected",
+    [
+        ("INBOX", "inbox"),
+        ("inbox", "inbox"),
+        ("Sent", "sent"),
+        ("Wysłane", "sent"),  # Polish
+        ("Elementy wysłane", "sent"),
+        ("Gesendet", "sent"),  # German
+        ("Drafts", "drafts"),
+        ("Robocze", "drafts"),
+        ("Trash", "trash"),
+        ("Kosz", "trash"),  # Polish
+        ("Papierkorb", "trash"),  # German
+        ("Spam", "junk"),
+        ("Junk", "junk"),
+        ("Archive", "archive"),
+        ("Archiwum", "archive"),
+        ("INBOX/Sent", "sent"),  # nested leaf
+        ("Work", None),
+        ("Random Folder", None),
+    ],
+)
+def test_infer_special_use(path: str, expected: str | None) -> None:
+    assert infer_special_use(path) == expected