Fix dashboard failing to load episodes after RSS import

The root cause was that modernc.org/sqlite stores time.Time as strings
but cannot scan strings back into time.Time, causing ListEpisodes to
fail. Changed PublishedAt and CreatedAt in store structs from time.Time
to string, with format/parse handled at the application level.

Also fixed a secondary issue where the published_at format stored during
import had a duplicated timezone offset.

store/store.go

@@ -2,7 +2,6 @@ package store
 
 import (
 	"database/sql"
-	"time"
 
 	_ "modernc.org/sqlite"
 )
@@ -15,7 +14,7 @@ type User struct {
 	PodcastSlug   string
 	PodcastImage  string
 	PodcastAuthor string
-	CreatedAt     time.Time
+	CreatedAt     string
 }
 
 type Episode struct {
@@ -25,8 +24,8 @@ type Episode struct {
 	Description string
 	AudioPath   string
 	ImagePath   string
-	PublishedAt time.Time
-	CreatedAt   time.Time
+	PublishedAt string
+	CreatedAt   string
 }
 
 type Store struct {
@@ -173,7 +172,7 @@ func (s *Store) GetEpisode(id int64) (*Episode, error) {
 	return e, nil
 }
 
-func (s *Store) CreateEpisode(userID int64, title, description, audioPath, imagePath string, publishedAt time.Time) (int64, error) {
+func (s *Store) CreateEpisode(userID int64, title, description, audioPath, imagePath, publishedAt string) (int64, error) {
 	res, err := s.db.Exec("INSERT INTO episodes (user_id, title, description, audio_path, image_path, published_at) VALUES (?, ?, ?, ?, ?, ?)",
 		userID, title, description, audioPath, imagePath, publishedAt)
 	if err != nil {
@@ -182,7 +181,7 @@ func (s *Store) CreateEpisode(userID int64, title, description, audioPath, image
 	return res.LastInsertId()
 }
 
-func (s *Store) UpdateEpisode(id int64, title, description, audioPath, imagePath string, publishedAt time.Time) error {
+func (s *Store) UpdateEpisode(id int64, title, description, audioPath, imagePath, publishedAt string) error {
 	_, err := s.db.Exec("UPDATE episodes SET title=?, description=?, audio_path=?, image_path=?, published_at=? WHERE id=?",
 		title, description, audioPath, imagePath, publishedAt, id)
 	return err