Fix Critical Security Issue: Replace print() with proper logging

Replaced all debug print() statements with proper logging framework:
- tasks/views.py: 5 print statements → logger.debug()
- sync/views.py: 15 print statements → logger.debug()
- config/celery.py: 1 print statement → logger.debug()
- notifications/tasks.py: 2 print statements → logger.error()

Retained print() in settings files (development.py, selfhosted.py) as they are appropriate warnings to stderr for configuration issues.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tasks/views.py

@@ -2,6 +2,7 @@
 Task views for KeepItGoing.
 """
 
+import logging
 from django.contrib.auth.decorators import login_required
 from django.db.models import Q
 from django.shortcuts import render, redirect, get_object_or_404
@@ -22,6 +23,8 @@ from .serializers import (
     TaskShareSerializer,
 )
 
+logger = logging.getLogger(__name__)
+
 
 # =============================================================================
 # API Views
@@ -553,7 +556,7 @@ def task_detail_partial(request, task_id):
 def web_timer_start(request, task_id):
     """Start a timer for a task (web view)."""
     task = get_object_or_404(Task, id=task_id, user=request.user)
-    print(f"[WEB TIMER DEBUG] Starting timer for task: {task.title} (id: {task_id})")
+    logger.debug(f"Starting timer for task: {task.title} (id: {task_id})")
 
     # Stop any existing running timer first (properly to calculate duration)
     running_entries = TimeEntry.objects.filter(
@@ -567,7 +570,7 @@ def web_timer_start(request, task_id):
         entry.save()  # This will calculate duration_seconds
         stopped_count += 1
 
-    print(f"[WEB TIMER DEBUG] Stopped {stopped_count} existing timers")
+    logger.debug(f"Stopped {stopped_count} existing timers")
 
     # Create new timer
     entry = TimeEntry.objects.create(
@@ -575,7 +578,7 @@ def web_timer_start(request, task_id):
         user=request.user,
         started_at=timezone.now()
     )
-    print(f"[WEB TIMER DEBUG] Created new timer entry: {entry.id}")
+    logger.debug(f"Created new timer entry: {entry.id}")
 
     next_url = request.POST.get('next', 'dashboard')
     return redirect(next_url)
@@ -585,7 +588,7 @@ def web_timer_start(request, task_id):
 @require_POST
 def web_timer_stop(request, task_id):
     """Stop a timer for a task (web view)."""
-    print(f"[WEB TIMER DEBUG] Stopping timer for task_id: {task_id}")
+    logger.debug(f"Stopping timer for task_id: {task_id}")
 
     # Get the running timer and stop it properly (to trigger save() and calculate duration)
     entries = TimeEntry.objects.filter(
@@ -600,7 +603,7 @@ def web_timer_stop(request, task_id):
         entry.save()  # This will calculate duration_seconds
         stopped_count += 1
 
-    print(f"[WEB TIMER DEBUG] Stopped {stopped_count} timer entries")
+    logger.debug(f"Stopped {stopped_count} timer entries")
 
     next_url = request.POST.get('next', 'dashboard')
     return redirect(next_url)