Add the HTTP hardening the policy requires before 1.0 (closes #108)

Every answer carries the six security headers REPO_POLICIES.md lists.
The Content-Security-Policy allows inline content only with a nonce made
for that answer; the pages put it on their style and script blocks and
drop their four style attributes.

The request log and /ip/ take a forwarded address only from a proxy
listed in TRUSTED_PROXIES, which stops the start when set but invalid:
the last X-Forwarded-For entry that is not a trusted proxy. X-Real-IP
and True-Client-IP are no longer read.

The JSON routes and the health check send fixed messages in place of
database, parser and resolver errors, and log the detail.

Model: opus-5-5

internal/templates/status.html

@@ -4,7 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>RouteWatch Status</title>
-    <style>
+    <style nonce="{{.CSPNonce}}">
         * {
             box-sizing: border-box;
         }
@@ -130,6 +130,7 @@
             color: #ef4444;
         }
         .error {
+            display: none;
             background: #fee;
             color: #c00;
             padding: 10px;
@@ -173,7 +174,7 @@
     </nav>
 
     <main class="main-content">
-    <div id="error" class="error" style="display: none;"></div>
+    <div id="error" class="error"></div>
     <div class="status-grid">
         <div class="status-card">
             <h2>RouteWatch</h2>
@@ -383,8 +384,8 @@
     <div id="handler-stats-container" class="status-grid">
         <!-- Handler stats will be dynamically added here -->
     </div>
-    
-    <script>
+
+    <script nonce="{{.CSPNonce}}">
         function formatBytes(bytes) {
             if (bytes === 0) return '0 B';
             const k = 1024;