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

pkg/util/password_test.go

@@ -0,0 +1,23 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package util
+
+import "testing"
+
+func TestDummyCheckPasswordDoesNotPanic(t *testing.T) {
+	DummyCheckPassword("any-password")
+}
+
+func TestCheckPasswordHashRoundTrip(t *testing.T) {
+	hash, err := HashPassword("secret-pass")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !CheckPasswordHash(hash, "secret-pass") {
+		t.Fatal("expected matching password to succeed")
+	}
+	if CheckPasswordHash(hash, "other-pass") {
+		t.Fatal("expected mismatched password to fail")
+	}
+}