feat: harden notification stack and switch logging selectors to icon grid

Notifications:
- Add shared http_base, redact, and SSRF hardening modules
- Refactor dispatcher, queue, receiver and per-provider clients
  (telegram, discord, email, matrix, ntfy, slack, webhook) to use
  the shared base, with bounded queue and redacted error logs
- Tests for ssrf, redact, http_base, queue bounds, dispatcher
  aggregation, telegram media partition, email and matrix clients

Frontend:
- Settings: log level / log format selectors now use IconGridSelect
  with per-option icons and i18n descriptions
- Minor providers page and entity-cache store updates

Tooling:
- Document code-review-graph MCP usage in CLAUDE.md
- Ignore .code-review-graph/, register .mcp.json

frontend/src/lib/stores/caches.svelte.ts

@@ -112,6 +112,34 @@ export const capabilitiesCache = (() => {
 	};
 })();
 
+/** Configured external base URL — used to render absolute webhook URLs.
+ *  Available to all authenticated users. Empty string when unset. */
+export const externalUrlCache = (() => {
+	let data = $state<string>('');
+	let fetchedAt = $state(0);
+	let inflight: Promise<string> | null = null;
+	const TTL = 300_000;
+	return {
+		get value() { return data; },
+		invalidate() { fetchedAt = 0; },
+		async fetch(force = false): Promise<string> {
+			if (!force && fetchedAt > 0 && Date.now() - fetchedAt < TTL) return data;
+			if (inflight) return inflight;
+			inflight = (async () => {
+				try {
+					const res = await api<{ external_url: string }>('/settings/external-url');
+					data = (res?.external_url || '').replace(/\/+$/, '');
+					fetchedAt = Date.now();
+					return data;
+				} finally {
+					inflight = null;
+				}
+			})();
+			return inflight;
+		},
+	};
+})();
+
 /** Supported template locales — fetched from app settings. */
 export const supportedLocalesCache = (() => {
 	let data = $state<string[]>(['en', 'ru']);