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/sqlite-federation/src/activity.rs

@@ -3,7 +3,8 @@ use async_trait::async_trait;
 use chrono::Utc;
 use k_ap::ActivityRepository;
 
-use super::{SqliteFederationRepository, datetime_to_str};
+use adapter_common::datetime_to_str;
+use super::SqliteFederationRepository;
 
 #[async_trait]
 impl ActivityRepository for SqliteFederationRepository {