Add Done button, tablet controls, super admin management, midnight strike reset, and activity log improvements

- Done button snaps block to full duration, marks complete, logs "Marked Done by User"; Reset after Done fully un-completes the block
- Session action buttons stretch full-width and double height for tablet tapping
- Super admin: reset password, disable/enable accounts, delete user (with cascade), last active date per user's timezone
- Disabled account login returns specific error message instead of generic invalid credentials
- Users can change own password from Admin → Settings
- Strikes reset automatically at midnight in user's configured timezone (lazy reset on page load)
- Break timer state fully restored when navigating away and back to dashboard
- Timer no longer auto-starts on navigation if it wasn't running before
- Implicit pause guard: no duplicate pause events when switching already-paused blocks or starting a break
- Block selection events removed from activity log; all event types have human-readable labels
- House emoji favicon via inline SVG data URI
- README updated to reflect all changes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/routers/children.py

@@ -1,3 +1,6 @@
+from datetime import datetime, timezone
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+
 from fastapi import APIRouter, Depends, HTTPException, status
 from pydantic import BaseModel, Field
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -13,6 +16,15 @@ from app.websocket.manager import manager
 router = APIRouter(prefix="/api/children", tags=["children"])
 
 
+def _today_in_tz(tz_name: str):
+    """Return today's date in the given IANA timezone, falling back to UTC."""
+    try:
+        tz = ZoneInfo(tz_name)
+    except (ZoneInfoNotFoundError, Exception):
+        tz = timezone.utc
+    return datetime.now(tz).date()
+
+
 @router.get("", response_model=list[ChildOut])
 async def list_children(
     current_user: User = Depends(get_current_user),
@@ -21,7 +33,20 @@ async def list_children(
     result = await db.execute(
         select(Child).where(Child.user_id == current_user.id).order_by(Child.name)
     )
-    return result.scalars().all()
+    children = result.scalars().all()
+
+    today = _today_in_tz(current_user.timezone)
+    needs_commit = False
+    for child in children:
+        if child.strikes != 0 and child.strikes_last_reset != today:
+            child.strikes = 0
+            child.strikes_last_reset = today
+            needs_commit = True
+            await manager.broadcast(child.id, {"event": "strikes_update", "strikes": 0})
+    if needs_commit:
+        await db.commit()
+
+    return children
 
 
 @router.post("", response_model=ChildOut, status_code=status.HTTP_201_CREATED)