Security hardening: fix SQL injection, WAF bypass, placeholder injection, and more

- C1: Replace all ClickHouse string interpolation with parameterized queries
  (query_params) to eliminate SQL injection in analytics endpoints
- C3: Strip Caddy placeholder patterns from redirect rules, protected paths,
  and Authentik auth endpoint to prevent config injection
- C4: Replace WAF custom directive blocklist with allowlist approach — only
  SecRule/SecAction/SecMarker/SecDefaultAction permitted; block ctl:ruleEngine
  and Include directives
- H2: Validate GCM authentication tag is exactly 16 bytes before decryption
- H3: Validate forward auth redirect URIs (scheme, no credentials) to prevent
  open redirects
- H4: Switch 11 analytics/WAF/geoip endpoints from session-only requireAdmin
  to requireApiAdmin supporting both Bearer token and session auth
- H5: Add input validation for instance-mode (whitelist) and sync-token
  (32-char minimum) in settings API
- M1: Add non-root user to l4-port-manager Dockerfile
- M5: Document Caddy admin API binding security rationale
- Document C2 (custom config injection) and H1 (SSRF via upstreams) as
  intentional admin features

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/models/forward-auth.ts

@@ -22,6 +22,20 @@ function hashToken(raw: string): string {
 // Store redirect URIs server-side so the client only holds an opaque ID.
 
 export async function createRedirectIntent(redirectUri: string): Promise<string> {
+  // Validate redirect URI to prevent open redirects
+  let parsed: URL;
+  try {
+    parsed = new URL(redirectUri);
+  } catch {
+    throw new Error("Invalid redirect URI");
+  }
+  if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
+    throw new Error("Redirect URI must use http or https scheme");
+  }
+  if (parsed.username || parsed.password) {
+    throw new Error("Redirect URI must not contain credentials");
+  }
+
   const rid = randomBytes(16).toString("hex");
   const ridHash = hashToken(rid);
   const now = nowIso();