feat(backend): implement comments, image uploads, and data consistency

Implement additional backend features and improve data models:

Comments System:
- Create Comment model with user and post relationships
- Add comments routes: GET /api/posts/:postId/comments (paginated), POST (create), DELETE (own comments)
- Update Post model with commentsCount field
- Emit Socket.IO events for newComment and commentDeleted
- Pagination support for comment lists
- Authorization checks (users can only delete own comments)
- 500 character limit on comments

Image Upload System:
- Implement Cloudinary configuration (config/cloudinary.js)
- Add uploadImage() and deleteImage() helper functions
- Image optimization: max 1000x1000, auto quality, auto format (WebP)
- Integrate image upload in users routes (profile pictures)
- Integrate image upload in posts routes (post images with add/update endpoints)
- File validation: 5MB limit, JPG/PNG/GIF/WebP only
- Automatic image deletion when removing posts/reports

Data Consistency Improvements:
- Add cascade deletes in Street model (remove from user, delete associated tasks)
- Add cascade deletes in Task model (remove from user completedTasks)
- Add cascade deletes in Post model (remove from user posts)
- Update user relationships on save (adoptedStreets, completedTasks, posts, events)
- Add proper indexes for performance (2dsphere for location, compound indexes)
- Add virtual relationships and toJSON configurations

Model Updates:
- Street: Add cascade hooks, location 2dsphere index
- Task: Add cascade hooks, compound indexes for queries
- Post: Add imageUrl, cloudinaryPublicId, commentsCount fields
- Event: Add participants tracking
- Report: Add image upload support
- User: Add earnedBadges virtual, profilePicture, cloudinaryPublicId

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

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

backend/models/Event.js

@@ -13,6 +13,7 @@ const EventSchema = new mongoose.Schema(
     date: {
       type: Date,
       required: true,
+      index: true,
     },
     location: {
       type: String,
@@ -24,10 +25,19 @@ const EventSchema = new mongoose.Schema(
         ref: "User",
       },
     ],
+    status: {
+      type: String,
+      enum: ["upcoming", "ongoing", "completed", "cancelled"],
+      default: "upcoming",
+      index: true,
+    },
   },
   {
     timestamps: true,
   },
 );
 
+// Index for querying upcoming events
+EventSchema.index({ date: 1, status: 1 });
+
 module.exports = mongoose.model("Event", EventSchema);