Feat: Backend Implementation for Image deletion

### Describe the feature

**Continuation of #802 – Add Context Menu (Right-Click) Actions for Images**

### Backend:

- Has no API to delete images
- Does not remove files from disk
- Does not clean up database records or thumbnails
- This results in an incomplete and misleading UX.

### Problem

**There is no end-to-end flow for deleting an image:**

- No backend endpoint for deletion
- No filesystem cleanup
- No database cleanup
- Frontend delete button not wired to any API
- Deleted images can reappear after refresh or restart

### Goal

1. Implement complete image deletion support, including:
2. Backend API to delete images safely
3. Frontend wiring to trigger deletion
4. Proper cleanup of files, thumbnails, and database records
5. Gallery refresh after deletion

### Expected Behavior

**When a user clicks Delete Image from the context menu:**
**Frontend sends delete request to backend**

### Backend:

1. Deletes image file from disk
2. Deletes thumbnail / cached files
3. Removes image record from database
4. Frontend updates gallery state immediately

**Proper error handling if:**

File is missing
File is locked
DB record does not exist

### Scope
**Backend (Primary)**

### Files to Update / Create

Backend (Python)

**Update**
```
backend/app/routes/images.py

backend/app/database/images.py

backend/app/utils/images.py (if helper required)

// Add (if needed)

backend/app/schemas/delete_image.py
```

### Frontend (Minimal Changes)

**Update**

- Context menu delete handler (existing UI)
- Gallery state refresh logic
- API Proposal

### Preferred REST-style endpoint:
```
DELETE /images/{image_id}
```

#### Alternative (if path-based deletion is required):
```
POST /images/delete
Body: { image_id | image_path }
```

### Acceptance Criteria ( Important)

- Image file is removed from disk
- Thumbnail/cached files are removed
- Database record is deleted
- Image does not reappear after refresh/restart
- UI updates instantly after deletion
- Safe error handling

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on this issue

### Add ScreenShots

## Demo video related to solution

https://github.com/user-attachments/assets/79634ffa-14b4-4a1a-af04-354505e0fa8f

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on this issue