Productivity features, UI translations, local email translation

- Snooze (with a Snoozed folder), keyboard shortcuts with a Settings
  section, mail templates (Compose > More > Templates), a Subscriptions
  folder with bulk unsubscribe/delete, and tracker blocking with a
  Privacy toggle (on by default)
- Own dialogs instead of browser popups; emoji picker in compose; compose
  windows survive a visit to Settings
- Sentence completion learned from the user's sent mail (no AI)
- Interface in English and Polish (one file per language, English as the
  fallback), picked from the browser on first run, then kept
- Email translation on the server via LibreTranslate: Translate button
  and "Translate to...", messages in several languages translated part
  by part, names/addresses/emoji/file names/phone numbers kept, an
  animated line while translating
- Antispam "Mark as spam" loads with the message, not when the menu opens

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/tests/indexer/test_sanitize.py

@@ -4,6 +4,8 @@ from __future__ import annotations
 
 import uuid
 
+import pytest
+
 from app.indexer.sanitize import sanitize_html
 
 MID = uuid.uuid4()
@@ -99,3 +101,72 @@ def test_script_content_still_stripped_with_style_allowed() -> None:
     result = sanitize_html(html, MID)
     assert "alert(1)" not in result.html
     assert ".a{color:red}" in result.html
+
+
+# --- Tracking pixels ---------------------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "tag",
+    [
+        '<img src="https://t.example.com/o.gif?u=1" width="1" height="1">',
+        '<img src="https://t.example.com/o.gif" width="1px" height="1px" border="0">',
+        "<img src='https://t.example.com/x' style='width:1px;height:1px'>",
+        '<img src="https://t.example.com/x" style="display:none">',
+        '<img src="https://x.list-manage.com/track/open.php?u=1&id=2">',
+        '<img src="https://u1.ct.sendgrid.net/wf/open?upn=abc" alt="">',
+        '<img src="https://mailtrack.io/trace/mail/abc.png">',
+        # Squeezed to a pixel by max-width, its height following.
+        '<img src="https://x.example/p.heic" width="1" height="1" '
+        'style="display:block; height:auto; max-width:1px !important; width:100%">',
+        '<img src="https://x.example/p" width="0" height="0" style="border:0;width:0;height:0;">',
+    ],
+)
+def test_tracking_pixels_are_removed_and_counted(tag: str) -> None:
+    html = f"<p>Hello</p>{tag}<p>Bye</p>"
+    for allow in (False, True):
+        result = sanitize_html(html, MID, allow_remote_images=allow)
+        assert result.trackers_blocked == 1
+        assert "<img" not in result.html
+        assert "Hello" in result.html and "Bye" in result.html
+    # A pixel alone is no reason to offer "Load images".
+    assert sanitize_html(html, MID).has_remote_images is False
+
+
+@pytest.mark.parametrize(
+    "tag",
+    [
+        '<img src="https://cdn.example.com/logo.png" width="180" height="47">',
+        '<img src="https://cdn.example.com/photo.jpg">',
+        '<img src="https://cdn.example.com/spacer.gif" width="1" height="40">',
+        '<img src="cid:logo" width="1" height="1">',
+        # Outlook signature logos: sizes in inches, not pixels.
+        '<img width="30" height="30" style="width:0.3125in; height:0.3125in" '
+        'src="https://pfx.tv/img/sig/logo.png">',
+        '<img style="width:1.5em;height:1.5em" src="https://cdn.example.com/icon.png">',
+        '<img style="width:1%;height:1%" src="https://cdn.example.com/bar.png">',
+        '<img style="width:1pt;height:1pt" src="https://cdn.example.com/dot.png">',
+        # Attributes say 1x1, the style draws it full width.
+        '<img src="https://cdn.example.com/photo.jpg" width="1" height="1" '
+        'style="width:100%;height:auto">',
+    ],
+)
+def test_real_images_are_kept(tag: str) -> None:
+    result = sanitize_html(f"<p>x</p>{tag}", MID, allow_remote_images=True)
+    assert result.trackers_blocked == 0
+    assert "<img" in result.html
+
+
+@pytest.mark.parametrize("size", [".", "1.2.3", "..", "", "px", "1e3", "-1"])
+def test_malformed_sizes_never_break_sanitizing(size: str) -> None:
+    tag = f'<img src="https://cdn.example.com/a.png" width="{size}" height="{size}">'
+    result = sanitize_html(f"<p>x</p>{tag}", MID, allow_remote_images=True)
+    assert result.trackers_blocked == 0
+    css = f'<img src="https://cdn.example.com/a.png" style="width:{size}px;height:{size}px">'
+    assert sanitize_html(css, MID, allow_remote_images=True).trackers_blocked == 0
+
+
+def test_tracker_blocking_can_be_switched_off() -> None:
+    tag = '<img src="https://t.example.com/o.gif" width="1" height="1">'
+    kept = sanitize_html(f"<p>x</p>{tag}", MID, allow_remote_images=True, block_trackers=False)
+    assert kept.trackers_blocked == 0 and "t.example.com/o.gif" in kept.html