add: SQLite-backed structured logging with retention

Replace JSON/file logging with a logs.db (WAL) store. Thread the logger
through the encoder and metadata client for debug instrumentation of every
ffmpeg/ffprobe/opusenc invocation and OMDb/TVmaze request. API keys are
redacted before request URLs are logged. Retention defaults to 7 days,
overridable via log_retention_days in config.

pkg/types/types.go

@@ -1,9 +1,5 @@
 package types
 
-import (
-	"time"
-)
-
 type MediaType string
 
 const (
@@ -36,9 +32,10 @@ type Metadata struct {
 }
 
 type Config struct {
-	OMDBAPIKey string `yaml:"omdb_api_key"`
-	Encoding   EncodingConfig
-	Paths      PathsConfig
+	OMDBAPIKey       string `yaml:"omdb_api_key"`
+	LogRetentionDays int    `yaml:"log_retention_days"`
+	Encoding         EncodingConfig
+	Paths            PathsConfig
 }
 
 type EncodingConfig struct {
@@ -60,11 +57,3 @@ type PathsConfig struct {
 	Failed    string `yaml:"failed"`
 	Work      string `yaml:"work"`
 }
-
-type LogEntry struct {
-	Timestamp time.Time `json:"timestamp"`
-	Level     string    `json:"level"`
-	Message   string    `json:"message"`
-	File      string    `json:"file,omitempty"`
-	Error     string    `json:"error,omitempty"`
-}