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-federation/src/lib.rs

@@ -12,14 +12,9 @@ mod watchlist;
 pub use ap_content::PostgresApContentQuery;
 pub use remote_goals::PostgresRemoteGoalRepository;
 
-use chrono::NaiveDateTime;
 use k_ap::{FollowerStatus, RemoteActor};
 use sqlx::{PgPool, Row};
 
-pub(crate) fn datetime_to_str(dt: &NaiveDateTime) -> String {
-    dt.format("%Y-%m-%d %H:%M:%S").to_string()
-}
-
 pub(crate) fn status_to_str(status: &FollowerStatus) -> &'static str {
     match status {
         FollowerStatus::Pending => "pending",