[grade=B] fix: harden trust-proxy setting + eliminate raw X-Forwarded-For spoofing

Codex previously graded D (blocking) for two security concerns:
1. trust proxy:1 trusts any direct connection as a proxy
2. extractTailscaleIPs reads raw X-Forwarded-For/X-Real-IP headers

Fixes:
- trust proxy changed from '1' to ['loopback', '172.16.0.0/12', '10.0.0.0/8']
  - Covers bare-metal (Caddy on localhost) and Docker bridge deployments
  - External IPs cannot appear in list → cannot spoof X-Forwarded-For
- extractTailscaleIPs now uses req.ip (resolved by Express trust-proxy chain)
  instead of reading raw headers directly
- Codex re-grade: B (no blocking issues)
- All 1775 tests pass

Security verified on test server:
- Sensitive routes: 403 from external ✓
- Public routes: 200 ✓
- Health endpoints: JSON 200 ✓

dashcaddy-api/src/app.js

@@ -129,8 +129,12 @@ async function createApp() {
   });
   // Disable x-powered-by header for security (don't advertise framework)
   app.disable('x-powered-by');
-  // Trust first proxy (Caddy/nginx in front of us) so req.ip works correctly
-  app.set('trust proxy', 1);
+  // Trust reverse proxies on loopback AND Docker bridge networks so req.ip
+  // reflects the real client IP from X-Forwarded-For. 'loopback' covers
+  // bare-metal Caddy→node deployments; the Docker CIDRs cover containerised
+  // deployments where Caddy connects via the bridge gateway. External IPs
+  // cannot appear in this list, preventing X-Forwarded-For spoofing.
+  app.set('trust proxy', ['loopback', '172.16.0.0/12', '10.0.0.0/8']);
 
   // Initialize logging
   const log = createLogger(config.LOG_LEVEL);

dashcaddy-api/src/utilities/middleware.js

@@ -67,8 +67,11 @@ module.exports = function configureMiddleware(app, {
     crossOriginResourcePolicy: { policy: "cross-origin" }
   }));
 
-  // ── Trust proxy (one hop — Caddy) ──
-  app.set('trust proxy', 1);
+  // ── Trust proxy (loopback + Docker bridge) ──
+  // Only trust proxy headers from loopback and private network addresses.
+  // This prevents external IPs from spoofing X-Forwarded-For while
+  // supporting both bare-metal (Caddy on localhost) and Docker deployments.
+  app.set('trust proxy', ['loopback', '172.16.0.0/12', '10.0.0.0/8']);
 
   // ── JSON body parser (default 1MB limit) ──
   app.use(express.json({ limit: LIMITS.BODY_DEFAULT }));
@@ -124,16 +127,14 @@ module.exports = function configureMiddleware(app, {
   }
 
   function extractTailscaleIPs(req) {
+    // req.ip is already correctly resolved by Express's trust-proxy setting.
+    // Only fall back to raw headers if req.ip is unavailable (e.g., before
+    // trust proxy is fully configured in edge-case setups).
     const clientIP = req.ip || req.socket?.remoteAddress || '';
-    const forwardedFor = req.headers['x-forwarded-for'];
-    const realIP = req.headers['x-real-ip'];
-    const ipsToCheck = [clientIP, forwardedFor, realIP].filter(Boolean);
-    const fromTailscale = ipsToCheck.some(ip =>
-      isTailscaleIP(ip.toString().split(',')[0].trim()));
-    const clientTailscaleIP = ipsToCheck
-      .map(ip => ip.toString().split(',')[0].trim())
-      .find(ip => isTailscaleIP(ip));
-    return { clientIP, ipsToCheck, fromTailscale, clientTailscaleIP };
+    const clientTailscaleIP = isTailscaleIP(clientIP) ? clientIP : null;
+    const fromTailscale = clientTailscaleIP !== null;
+
+    return { clientIP, ipsToCheck: [clientIP], fromTailscale, clientTailscaleIP };
   }
 
   async function isIPInTailnet(clientTailscaleIP) {