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/like.go

@@ -0,0 +1,16 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package util
+
+import "strings"
+
+var likeEscaper = strings.NewReplacer(`\`, `\\`, `%`, `\%`, `_`, `\_`)
+
+// EscapeLike escapes SQL LIKE metacharacters (\, %, _) so a user-supplied
+// value matches literally in LIKE patterns. Pair it with an explicit
+// `ESCAPE '\'` clause where the dialect has no backslash default (SQLite);
+// PostgreSQL and ClickHouse treat backslash as the default LIKE escape.
+func EscapeLike(value string) string {
+	return likeEscaper.Replace(value)
+}