cleanup: strip comments, extract constants, DRY shared helpers across adapters + infra-wiring

- strip all comments except WHY workaround notes (3 remain)
- remove all #[allow(dead_code)]; fix via _prefix rename
- extract named constants: JWT time units, token types, default config values, jellyfin fallback bitrate
- DRY: move serialize_enum_as_string, content_type_str, parse_content_type, parse_genres_blob to adapter-common
- sqlite+postgres library.rs use shared helpers instead of local copies
- sqlite+postgres channel.rs use shared serialize_enum_as_string
- remove dead `let _ = ext` in scanner.rs

crates/adapters/sqlite/src/schedule.rs

@@ -1,5 +1,3 @@
-//! SQLite adapter for schedule persistence (ScheduleCommand + ScheduleQuery).
-
 use std::collections::HashMap;
 
 use async_trait::async_trait;
@@ -22,8 +20,6 @@ impl SqliteScheduleRepository {
     }
 }
 
-// -- Row types ---------------------------------------------------------------
-
 #[derive(Debug, sqlx::FromRow)]
 struct ScheduleRow {
     id: String,
@@ -36,8 +32,7 @@ struct ScheduleRow {
 #[derive(Debug, sqlx::FromRow)]
 struct SlotRow {
     id: String,
-    #[allow(dead_code)]
-    schedule_id: String,
+    _schedule_id: String,
     start_at: String,
     end_at: String,
     item: String,
@@ -59,8 +54,6 @@ struct PlaybackRecordRow {
     generation: i64,
 }
 
-// -- Mapping -----------------------------------------------------------------
-
 fn map_slot_row(row: SlotRow) -> DomainResult<ScheduledSlot> {
     let id = SlotId::from_uuid(parse_uuid(&row.id, "slot id")?);
     let source_block_id = BlockId::from_uuid(parse_uuid(&row.source_block_id, "block id")?);
@@ -103,8 +96,6 @@ fn map_playback_row(row: PlaybackRecordRow) -> DomainResult<PlaybackRecord> {
     ))
 }
 
-// -- Internal helpers --------------------------------------------------------
-
 impl SqliteScheduleRepository {
     async fn fetch_slots(&self, schedule_id: &str) -> DomainResult<Vec<SlotRow>> {
         sqlx::query_as(
@@ -118,8 +109,6 @@ impl SqliteScheduleRepository {
     }
 }
 
-// -- Command -----------------------------------------------------------------
-
 #[async_trait]
 impl ScheduleCommand for SqliteScheduleRepository {
     async fn save(&self, schedule: &GeneratedSchedule) -> DomainResult<()> {
@@ -142,7 +131,6 @@ impl ScheduleCommand for SqliteScheduleRepository {
         .await
         .map_err(map_sqlx_error)?;
 
-        // Delete-then-insert all slots
         sqlx::query("DELETE FROM scheduled_slots WHERE schedule_id = ?")
             .bind(schedule.id().value().to_string())
             .execute(&self.pool)
@@ -216,8 +204,6 @@ impl ScheduleCommand for SqliteScheduleRepository {
     }
 }
 
-// -- Query -------------------------------------------------------------------
-
 #[async_trait]
 impl ScheduleQuery for SqliteScheduleRepository {
     async fn find_active(