### Description
This pull request introduces the core functionality for creating and updating posts, completing the backend CRUD operations for the `post` feature. It includes new API endpoints, database schema changes, and corresponding updates across the entire application stack from the database layer to the frontend.
#### Backend API
- **Added new authenticated endpoints:**
- `POST /post`: To create a new post.
- `PUT /post/{id}`: To update an existing post.
- Implemented the full vertical slice for these operations, including:
- `CreatePostUseCase` and `UpdatePostUseCase`.
- Repository and DB service methods for creating, updating, and associating posts with labels.
- Transactional database operations to ensure data integrity when creating/updating posts and their associated labels.
#### Database
- Added a new migration to include an `"order"` column in the `post_label` table.
- This column preserves the user-defined order of labels for each post.
- Queries have been updated to fetch and sort labels based on this new column.
#### API Schema & Documentation
- Enhanced `utoipa` OpenAPI documentation with more specific formats for data types:
- `#[schema(format = Uri)]` for URLs like `preview_image_url`.
- `#[schema(format = Email)]` for user emails.
- `#[schema(format = DateTime)]` for timestamps.
- Standardized the `published_time` field to use the RFC3339 string format instead of a numeric timestamp, improving API clarity and interoperability.
#### Frontend
- Updated the `PostInfoResponseDto` in the frontend to correctly parse the new `DateTime` (ISO string) format for `published_time`.
#### Refactoring
- Renamed `get_full_post` to a more descriptive `get_post_by_id` across the post feature module for better code clarity.
### Package Changes
```toml
utoipa = { version = "5.4.0", features = [
"actix_extras",
"non_strict_integers",
"url",
] }
```
### Screenshots
_No response_
### Reference
Resolves#104
### Checklist
- [x] A milestone is set
- [x] The related issuse has been linked to this branch
Reviewed-on: #108
Co-authored-by: SquidSpirit <squid@squidspirit.com>
Co-committed-by: SquidSpirit <squid@squidspirit.com>
