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/Cargo.toml

@@ -12,6 +12,7 @@ sqlx = { version = "0.8.6", features = [
     "chrono",
 ] }
 activitypub = { workspace = true }
+adapter-common = { workspace = true }
 k-ap = { version = "0.4.1", registry = "gitea" }
 domain = { workspace = true }
 uuid = { workspace = true }