refactor: extract adapter-common crate — shared sqlx error mapping,

row-to-domain conversions, date/uuid utils

Eliminates 39 map_err copies, consolidates parse_uuid/parse_datetime/
datetime_to_str/format_year_month, extracts 7 shared row-to-domain
conversion functions (movie, review, watchlist, stats, user_summary).
Row structs stay per-adapter (FromRow is db-specific), only conversion
logic is shared. Net -281 lines.

crates/adapters/postgres/src/user_settings.rs

@@ -16,10 +16,6 @@ impl PostgresUserSettingsRepository {
         Self { pool }
     }
 
-    fn map_err(e: sqlx::Error) -> DomainError {
-        tracing::error!("Database error: {:?}", e);
-        DomainError::InfrastructureError("Database operation failed".into())
-    }
 }
 
 #[async_trait]
@@ -33,7 +29,7 @@ impl UserSettingsRepository for PostgresUserSettingsRepository {
         .bind(&uid)
         .fetch_optional(&self.pool)
         .await
-        .map_err(Self::map_err)?;
+        .map_err(adapter_common::map_sqlx_error)?;
 
         match row {
             Some(r) => {
@@ -65,7 +61,7 @@ impl UserSettingsRepository for PostgresUserSettingsRepository {
         .bind(settings.federate_watchlist())
         .execute(&self.pool)
         .await
-        .map_err(Self::map_err)?;
+        .map_err(adapter_common::map_sqlx_error)?;
         Ok(())
     }
 }
@@ -81,7 +77,7 @@ impl UserFederationSettingsQuery for PostgresUserSettingsRepository {
         .bind(&uid)
         .fetch_optional(&self.pool)
         .await
-        .map_err(Self::map_err)?;
+        .map_err(adapter_common::map_sqlx_error)?;
 
         match row {
             Some(r) => {