Add build script, AGENTS.md, fix formatting

- scripts/build: gofmt, go vet, go build, docker build
- AGENTS.md: agents must run ./scripts/build before committing
- Fix gofmt issues in handler/auth.go and store/store.go

store/store.go

@@ -8,13 +8,13 @@ import (
 )
 
 type User struct {
-	ID             int64
-	Email          string
-	PasswordHash   string
-	PodcastTitle   string
-	PodcastImage   string
-	PodcastAuthor  string
-	CreatedAt      time.Time
+	ID            int64
+	Email         string
+	PasswordHash  string
+	PodcastTitle  string
+	PodcastImage  string
+	PodcastAuthor string
+	CreatedAt     time.Time
 }
 
 type Episode struct {