Add event colors (Catppuccin Mocha) and read-only week view for users

Admins can now pick a color per event from a Catppuccin Mocha palette;
existing events default to blue. Colors flow through to both the admin
timeline and the new "Неделя" tab in the user view, which reuses the
admin's weekly grid in a read-only mode. Also reworks event blocks to
show a single-line "start–end title" so short events no longer overflow,
tidies the admin toolbar, and expands mobile responsiveness across both
frontends.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/api.py

@@ -115,7 +115,8 @@ async def create_item(
             start_time=event.start_time,
             duration_min=event.duration_min,
             title=event.title,
-            repeat_weekly=event.repeat_weekly
+            repeat_weekly=event.repeat_weekly,
+            color=event.color or "blue"
         )
         if event.repeat_weekly:
             new_event.weekday = get_weekday_from_date(event.date)
@@ -214,7 +215,8 @@ async def update_item(
             replacement_title=update.title or event.title,
             replacement_date=replacement_date,
             replacement_start_time=replacement_start_time,
-            replacement_duration_min=replacement_duration
+            replacement_duration_min=replacement_duration,
+            replacement_color=update.color or event.color
         ))
         await db.commit()
         return {"success": True, "action": "exception_created"}
@@ -237,6 +239,8 @@ async def update_item(
         event.start_time = update.start_time
     if update.duration_min:
         event.duration_min = update.duration_min
+    if update.color:
+        event.color = update.color
 
     await db.commit()
     return {"success": True}