feat(rate-limit): add default request rate limit configuration

- Support openresty_default_limit_req_per_ip in system_configs.
- Add limit_req and limit_req_status 429 directive generation in openresty renderer.
- Implement route-level limit_req_per_ip override and explicit disable.
- Add frontend UI inputs and validation in rate limits tab config.
- Update swagger API docs and changelog for v3.4.3-beta.3.

internal/db/migrator/goose/postgres/202607200001_add_openresty_default_limit_req_per_ip.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+INSERT INTO w_system_configs (key, value, type, visibility, description, created_at, updated_at)
+VALUES
+  ('openresty_default_limit_req_per_ip', '', 'business', 0, '默认单 IP 请求频率限制（空关闭，例如 10r/s、100r/m）', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+ON CONFLICT (key) DO NOTHING;
+
+ALTER TABLE w_of_proxy_routes ADD COLUMN limit_req_per_ip VARCHAR(32) NOT NULL DEFAULT '';
+
+-- +goose Down
+ALTER TABLE w_of_proxy_routes DROP COLUMN limit_req_per_ip;
+
+DELETE FROM w_system_configs WHERE key = 'openresty_default_limit_req_per_ip';

internal/db/migrator/goose/sqlite/202607200001_add_openresty_default_limit_req_per_ip.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+INSERT INTO w_system_configs (key, value, type, visibility, description, created_at, updated_at)
+VALUES
+  ('openresty_default_limit_req_per_ip', '', 'business', 0, '默认单 IP 请求频率限制（空关闭，例如 10r/s、100r/m）', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+ON CONFLICT (key) DO NOTHING;
+
+ALTER TABLE w_of_proxy_routes ADD COLUMN limit_req_per_ip VARCHAR(32) NOT NULL DEFAULT '';
+
+-- +goose Down
+ALTER TABLE w_of_proxy_routes DROP COLUMN limit_req_per_ip;
+
+DELETE FROM w_system_configs WHERE key = 'openresty_default_limit_req_per_ip';