feat(core): sync framework security hardening and accessibility improvements

- add util.Go with panic recovery for background goroutines
- add util.EscapeLike and explicit ESCAPE clause for SQL LIKE queries
- add DummyCheckPassword and subtle.ConstantTimeCompare against timing attacks
- enforce session ID rotation upon login/oauth callback to prevent session fixation
- add sliding window login failure rate limiting and oauth state rate limiting
- fix redis client capture race in pubsub listeners and wait on stop channel
- adjust global --primary to oklch(51.1% 0.262 276.966) for WCAG AA contrast
- fix semantic heading levels and missing aria-labels across UI components
- document security, concurrency, and a11y standards in AGENTS.md

internal/apps/oauth/errs.go

@@ -19,4 +19,5 @@ const (
 	errAuthSourceDisabled              = "认证源未启用"
 	errInvalidExternalAccountBindingID = "绑定记录 ID 无效"
 	ErrTokenAuthNotAllowed             = "该端点不允许使用访问令牌进行身份验证" //nolint:gosec // false positive: this is an error message, not hardcoded credentials
+	errOAuthStateRateLimited           = "请求授权过于频繁，请稍后重试"
 )