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/follow.rs

@@ -6,8 +6,9 @@ use k_ap::{
 };
 use sqlx::Row;
 
+use adapter_common::datetime_to_str;
 use super::{
-    PG_ACTOR_COLS, PostgresFederationRepository, datetime_to_str, pg_remote_actor, status_to_str,
+    PG_ACTOR_COLS, PostgresFederationRepository, pg_remote_actor, status_to_str,
     str_to_status,
 };