fix(admin): repair system maintenance controls

Implement server-side searchable user filtering for usage records, including backend search parameters and a shared frontend selector with loading, empty, and pinned-selected states.

Fix announcement deletion by cascading announcement read rows through a Postgres migration and defensive repository cleanup across supported backends.

Wire admin system purge and cleanup endpoints to real data deletion/maintenance flows, improve DataManagement messages, rebuild stats after stats purge, and add runtime OAuth token refresh maintenance when enabled.

Verified with rust-ci equivalent checks: cargo fmt, split clippy, split cargo tests, SQLite/Postgres/MySQL smoke tests, plus frontend npm ci, build, pages build, type-check, and targeted usage selector tests.

crates/aether-data/src/repository/users/postgres.rs

@@ -626,6 +626,22 @@ impl SqlxUserReadRepository {
         if let Some(is_active) = query.is_active {
             builder.push(" AND is_active = ").push_bind(is_active);
         }
+        if let Some(search) = query
+            .search
+            .as_deref()
+            .map(str::trim)
+            .filter(|value| !value.is_empty())
+        {
+            let pattern = format!("%{}%", search.to_ascii_lowercase());
+            builder
+                .push(" AND (LOWER(id) LIKE ")
+                .push_bind(pattern.clone())
+                .push(" OR LOWER(username) LIKE ")
+                .push_bind(pattern.clone())
+                .push(" OR LOWER(COALESCE(email, '')) LIKE ")
+                .push_bind(pattern)
+                .push(")");
+        }
 
         builder
             .push(" ORDER BY id ASC OFFSET ")