Add unified post storage.

Provide one creation path for roots and replies, recursive thread loading, body-only updates, root listings, and post voting across PostgreSQL and the in-memory test store.

internal/store/postgres_store.go

@@ -144,6 +144,32 @@ func (p *Postgres) UpsertAnswer(ctx context.Context, a *Answer) error {
 	return a.Upsert(ctx)
 }
 
+func (p *Postgres) CreatePost(ctx context.Context, post *Post) error {
+	post.db = p.db
+	return post.Create(ctx)
+}
+
+func (p *Postgres) GetPost(ctx context.Context, id string) (*Post, error) {
+	return GetPost(ctx, p.db, id)
+}
+
+func (p *Postgres) GetPostThread(ctx context.Context, rootID string) (*Post, error) {
+	return GetPostThread(ctx, p.db, rootID)
+}
+
+func (p *Postgres) UpdatePost(ctx context.Context, post *Post) error {
+	post.db = p.db
+	return post.Update(ctx)
+}
+
+func (p *Postgres) ListRootPosts(ctx context.Context, postDate, viewerID string) ([]Post, error) {
+	return ListRootPosts(ctx, p.db, postDate, viewerID)
+}
+
+func (p *Postgres) VotePost(ctx context.Context, userID, postID string, value int) error {
+	return SetPostVote(ctx, p.db, userID, postID, value)
+}
+
 func (p *Postgres) Vote(ctx context.Context, userID, questionID string, value int) error {
 	return Vote(ctx, p.db, userID, questionID, value)
 }