feat(translation): machine translation pipeline + admin bulk enqueue UI

- LibreTranslate client (chunks on blank lines, ≤4500 chars, 3-goroutine semaphore)
- Runner translation task loop (OTel, heartbeat, MinIO storage)
- PocketBase translation_jobs collection support (create/claim/finish/list)
- Per-chapter language switcher on chapter reader (EN/RU/ID/PT/FR, polls until done)
- Admin /admin/translation page: bulk enqueue form + live-polling jobs table
- New backend routes: POST /api/translation/{slug}/{n}, GET /api/translation/status,
  GET /api/translation/{slug}/{n}, GET /api/admin/translation/jobs,
  POST /api/admin/translation/bulk
- ListTranslationTasks added to taskqueue.Reader interface + store impl
- All builds and tests pass; svelte-check: 0 errors

backend/internal/config/config.go

@@ -46,6 +46,8 @@ type MinIO struct {
 	BucketAvatars string
 	// BucketBrowse is the bucket that holds cached browse page snapshots (JSON).
 	BucketBrowse string
+	// BucketTranslations is the bucket that holds machine-translated chapter markdown.
+	BucketTranslations string
 }
 
 // Kokoro holds connection settings for the Kokoro-FastAPI TTS service.
@@ -64,6 +66,16 @@ type PocketTTS struct {
 	URL string
 }
 
+// LibreTranslate holds connection settings for a self-hosted LibreTranslate instance.
+type LibreTranslate struct {
+	// URL is the base URL of the LibreTranslate instance, e.g. https://translate.libnovel.cc
+	// An empty string disables machine translation entirely.
+	URL string
+	// APIKey is the optional API key for the LibreTranslate instance.
+	// Leave empty if the instance runs without authentication.
+	APIKey string
+}
+
 // HTTP holds settings for the HTTP server (backend only).
 type HTTP struct {
 	// Addr is the listen address, e.g. ":8080"
@@ -107,6 +119,8 @@ type Runner struct {
 	MaxConcurrentScrape int
 	// MaxConcurrentAudio limits simultaneous audio-generation goroutines.
 	MaxConcurrentAudio int
+	// MaxConcurrentTranslation limits simultaneous translation goroutines.
+	MaxConcurrentTranslation int
 	// WorkerID is a unique identifier for this runner instance.
 	// Defaults to the system hostname.
 	WorkerID string
@@ -135,15 +149,16 @@ type Runner struct {
 
 // Config is the top-level configuration struct consumed by both binaries.
 type Config struct {
-	PocketBase  PocketBase
-	MinIO       MinIO
-	Kokoro      Kokoro
-	PocketTTS   PocketTTS
-	HTTP        HTTP
-	Runner      Runner
-	Meilisearch Meilisearch
-	Valkey      Valkey
-	Redis       Redis
+	PocketBase     PocketBase
+	MinIO          MinIO
+	Kokoro         Kokoro
+	PocketTTS      PocketTTS
+	LibreTranslate LibreTranslate
+	HTTP           HTTP
+	Runner         Runner
+	Meilisearch    Meilisearch
+	Valkey         Valkey
+	Redis          Redis
 	// LogLevel is one of "debug", "info", "warn", "error".
 	LogLevel string
 }
@@ -166,16 +181,17 @@ func Load() Config {
 		},
 
 		MinIO: MinIO{
-			Endpoint:       envOr("MINIO_ENDPOINT", "localhost:9000"),
-			PublicEndpoint: envOr("MINIO_PUBLIC_ENDPOINT", ""),
-			AccessKey:      envOr("MINIO_ACCESS_KEY", "admin"),
-			SecretKey:      envOr("MINIO_SECRET_KEY", "changeme123"),
-			UseSSL:         envBool("MINIO_USE_SSL", false),
-			PublicUseSSL:   envBool("MINIO_PUBLIC_USE_SSL", true),
-			BucketChapters: envOr("MINIO_BUCKET_CHAPTERS", "chapters"),
-			BucketAudio:    envOr("MINIO_BUCKET_AUDIO", "audio"),
-			BucketAvatars:  envOr("MINIO_BUCKET_AVATARS", "avatars"),
-			BucketBrowse:   envOr("MINIO_BUCKET_BROWSE", "catalogue"),
+			Endpoint:           envOr("MINIO_ENDPOINT", "localhost:9000"),
+			PublicEndpoint:     envOr("MINIO_PUBLIC_ENDPOINT", ""),
+			AccessKey:          envOr("MINIO_ACCESS_KEY", "admin"),
+			SecretKey:          envOr("MINIO_SECRET_KEY", "changeme123"),
+			UseSSL:             envBool("MINIO_USE_SSL", false),
+			PublicUseSSL:       envBool("MINIO_PUBLIC_USE_SSL", true),
+			BucketChapters:     envOr("MINIO_BUCKET_CHAPTERS", "chapters"),
+			BucketAudio:        envOr("MINIO_BUCKET_AUDIO", "audio"),
+			BucketAvatars:      envOr("MINIO_BUCKET_AVATARS", "avatars"),
+			BucketBrowse:       envOr("MINIO_BUCKET_BROWSE", "catalogue"),
+			BucketTranslations: envOr("MINIO_BUCKET_TRANSLATIONS", "translations"),
 		},
 
 		Kokoro: Kokoro{
@@ -195,6 +211,7 @@ func Load() Config {
 			PollInterval:                envDuration("RUNNER_POLL_INTERVAL", 30*time.Second),
 			MaxConcurrentScrape:         envInt("RUNNER_MAX_CONCURRENT_SCRAPE", 1),
 			MaxConcurrentAudio:          envInt("RUNNER_MAX_CONCURRENT_AUDIO", 1),
+			MaxConcurrentTranslation:    envInt("RUNNER_MAX_CONCURRENT_TRANSLATION", 1),
 			WorkerID:                    envOr("RUNNER_WORKER_ID", workerID),
 			Workers:                     envInt("RUNNER_WORKERS", 0), // 0 → runtime.NumCPU()
 			Timeout:                     envDuration("RUNNER_TIMEOUT", 90*time.Second),