Release secrets-mcp 0.3.0: folder/type schema and MCP folder disambiguation

- Rename namespace/kind to folder/type on entries, audit_log, and history tables;
  add notes. Unique key is (user_id, folder, name).
- Service layer and MCP tools support name-first lookup with optional folder when
  multiple entries share the same name.
- secrets_delete dry_run uses the same disambiguation as real deletes.
- Add scripts/migrate-v0.3.0.sql for manual DB migration. Refresh README and
  AGENTS.md.

Made-with: Cursor

crates/secrets-core/src/service/audit_log.rs

@@ -8,7 +8,7 @@ pub async fn list_for_user(pool: &PgPool, user_id: Uuid, limit: i64) -> Result<V
     let limit = limit.clamp(1, 200);
 
     let rows = sqlx::query_as(
-        "SELECT id, user_id, action, namespace, kind, name, detail, created_at \
+        "SELECT id, user_id, action, folder, type, name, detail, created_at \
          FROM audit_log \
          WHERE user_id = $1 \
          ORDER BY created_at DESC, id DESC \