clean: Article to Post in domain and related use cases

Renamed the 'Article' domain to 'Post' in order to better reflect the purpose and utility of the object. The change involved renaming all related use cases, classes, and other references from 'Article' to 'Post' and updating all functions and data types to work with Posts instead of Articles.

domain/article/article.go

@@ -1,37 +0,0 @@
-package article
-
-import "time"
-
-type Article struct {
-	ID        uint32    `json:"id"`
-	Title     string    `json:"title"`
-	Body      string    `json:"body"`
-	CreatedAt time.Time `json:"created_at"`
-	UpdatedAt time.Time `json:"updated_at"`
-}
-
-func FromApi(
-	title string,
-	body string,
-) Article {
-	return Article{
-		Title: title,
-		Body:  body,
-	}
-}
-
-func FromDb(
-	id uint32,
-	title string,
-	body string,
-	createdAt time.Time,
-	updatedAt time.Time,
-) Article {
-	return Article{
-		ID:        id,
-		Title:     title,
-		Body:      body,
-		CreatedAt: createdAt,
-		UpdatedAt: updatedAt,
-	}
-}