feat(web): theme import/export, more themable colors, hideable local/ical calendars

Theme:
- Export/import themes via UI as <date>_<time>.theme (JSON, readable keys,
  link to THEME.md). Import is partial-aware: only present params are written
  (server accepts partial); prompts before importing files with unknown params.
- Dynamic favicon + theme-color tinted to the primary colour on load/save.
- New themable colours: general hover-highlight, day hover/selected/bg,
  today background, plus two unified sidebar action-icon colours
  (inactive/active) covering bell, hide, delete and read-only icons.
- All new colours are per-setting syncable; documented in THEME.md.

UX:
- Styled confirm dialog (#modal-confirm) replaces window.confirm() for
  calendar delete and account disconnect.
- Birthday/local calendars and iCal subscriptions can now be hidden from the
  sidebar via Settings (new sidebar_hidden column + hide toggle).

Backend: additive nullable columns + idempotent migrations for user_settings
colours and local_calendars/ical_subscriptions.sidebar_hidden.

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

backend/routers/ical_router.py

@@ -31,6 +31,7 @@ class SubscriptionUpdate(BaseModel):
     url: Optional[str] = None
     color: Optional[str] = None
     enabled: Optional[bool] = None
+    sidebar_hidden: Optional[bool] = None
     refresh_minutes: Optional[int] = None
     reminders_enabled: Optional[bool] = None
 
@@ -42,6 +43,7 @@ def _sub_dict(sub: models.ICalSubscription) -> dict:
         "url": sub.url,
         "color": sub.color,
         "enabled": sub.enabled,
+        "sidebar_hidden": bool(sub.sidebar_hidden),
         "reminders_enabled": bool(sub.reminders_enabled),
         "refresh_minutes": sub.refresh_minutes,
         "last_fetched": sub.last_fetched.isoformat() if sub.last_fetched else None,
@@ -273,6 +275,8 @@ def update_subscription(
         sub.color = data.color
     if data.enabled is not None:
         sub.enabled = data.enabled
+    if data.sidebar_hidden is not None:
+        sub.sidebar_hidden = data.sidebar_hidden
     if data.refresh_minutes is not None:
         sub.refresh_minutes = data.refresh_minutes
     if data.reminders_enabled is not None:

backend/routers/local_router.py

@@ -33,6 +33,7 @@ class CalendarUpdate(BaseModel):
     name: Optional[str] = None
     color: Optional[str] = None
     enabled: Optional[bool] = None
+    sidebar_hidden: Optional[bool] = None
     reminders_enabled: Optional[bool] = None
     caldav_published: Optional[bool] = None
     is_birthday: Optional[bool] = None
@@ -88,6 +89,7 @@ def _cal_dict(cal: models.LocalCalendar, *, owned: bool = True,
         # A recipient's own colour for a shared calendar wins over the owner's.
         "color": color_override or cal.color,
         "enabled": cal.enabled,
+        "sidebar_hidden": bool(cal.sidebar_hidden),
         "reminders_enabled": bool(cal.reminders_enabled),
         "caldav_published": bool(cal.caldav_published),
         "is_birthday": bool(cal.is_birthday),
@@ -265,6 +267,8 @@ def update_calendar(
         cal.color = data.color
     if data.enabled is not None:
         cal.enabled = data.enabled
+    if data.sidebar_hidden is not None:
+        cal.sidebar_hidden = data.sidebar_hidden
     if data.reminders_enabled is not None:
         cal.reminders_enabled = data.reminders_enabled
     if data.is_birthday is not None:

backend/routers/settings_router.py

@@ -37,6 +37,13 @@ DEFAULT_SYNC = {
     "cache_months": False,
     "month_view_paged": False,
     "surface_color": False,
+    "hover_highlight_color": True,
+    "icon_inactive_color": True,
+    "icon_active_color": True,
+    "day_hover_color": True,
+    "day_selected_color": True,
+    "day_bg_color": True,
+    "today_bg_color": True,
 }
 
 
@@ -72,6 +79,13 @@ class SettingsUpdate(BaseModel):
     line_color: Optional[str] = None
     bg_color:   Optional[str] = None
     surface_color: Optional[str] = None
+    hover_highlight_color: Optional[str] = None
+    icon_inactive_color: Optional[str] = None
+    icon_active_color: Optional[str] = None
+    day_hover_color: Optional[str] = None
+    day_selected_color: Optional[str] = None
+    day_bg_color: Optional[str] = None
+    today_bg_color: Optional[str] = None
     private_event_visibility: Optional[str] = None
     group_visible_calendar_id: Optional[int] = None
     default_reminder_minutes: Optional[int] = None  # null = off
@@ -100,6 +114,13 @@ def _settings_dict(s: models.UserSettings) -> dict:
         "line_color": s.line_color,
         "bg_color":   s.bg_color,
         "surface_color": s.surface_color,
+        "hover_highlight_color": s.hover_highlight_color,
+        "icon_inactive_color": s.icon_inactive_color,
+        "icon_active_color": s.icon_active_color,
+        "day_hover_color": s.day_hover_color,
+        "day_selected_color": s.day_selected_color,
+        "day_bg_color": s.day_bg_color,
+        "today_bg_color": s.today_bg_color,
         "private_event_visibility": s.private_event_visibility or "busy",
         "group_visible_calendar_id": s.group_visible_calendar_id,
         "default_reminder_minutes": s.default_reminder_minutes,
@@ -165,7 +186,7 @@ def update_settings(
     # For these three override colours, an explicit null is meaningful
     # ("reset to default") and must be persisted as NULL. All other fields
     # keep the previous behaviour where a null/missing value is ignored.
-    NULLABLE_OVERRIDES = {"text_color", "line_color", "bg_color", "surface_color", "group_visible_calendar_id", "default_reminder_minutes", "default_event_duration_minutes", "share_calendar_icon"}
+    NULLABLE_OVERRIDES = {"text_color", "line_color", "bg_color", "surface_color", "hover_highlight_color", "icon_inactive_color", "icon_active_color", "day_hover_color", "day_selected_color", "day_bg_color", "today_bg_color", "group_visible_calendar_id", "default_reminder_minutes", "default_event_duration_minutes", "share_calendar_icon"}
     update_data = data.model_dump(exclude_unset=True)
 
     # Merge sync-flag overrides into the stored account-wide JSON map. Only known