Address follow-up review: cheaper avatars, list limits, less chatter.

Switch avatar resize to ApproxBiLinear, cap hunt/profile/admin list queries, drop redundant admin/profile lookups, dedupe CI on app PRs, and refresh stale todo.md notes.

db/queries/users.sql

@@ -15,7 +15,8 @@ WHERE username = $1;
 -- name: ListUsers :many
 SELECT id, username, name, role, avatar_url, state, created_at
 FROM users
-ORDER BY created_at ASC;
+ORDER BY created_at ASC
+LIMIT sqlc.arg(row_limit);
 
 -- name: CountAdmins :one
 SELECT COUNT(*)::bigint AS count