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/index.html

@@ -4,7 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>RouteWatch - BGP Route Monitor</title>
-    <style>
+    <style nonce="{{.CSPNonce}}">
         * {
             box-sizing: border-box;
         }
@@ -167,6 +167,13 @@
             color: #95a5a6;
             margin-top: 8px;
         }
+        #asname-results p {
+            color: #7f8c8d;
+            margin-top: 12px;
+        }
+        #asname-results .search-message {
+            font-size: 13px;
+        }
 
         /* IP Lookup result */
         .ip-result {
@@ -329,7 +336,7 @@
         <span><a href="{{appGitCommitURL}}">{{appGitRevision}}</a></span>
     </footer>
 
-    <script>
+    <script nonce="{{.CSPNonce}}">
         function formatNumber(num) {
             if (num >= 1000000) {
                 return (num / 1000000).toFixed(1) + 'M';
@@ -387,7 +394,7 @@
             if (!query) return;
 
             const resultsDiv = document.getElementById('asname-results');
-            resultsDiv.innerHTML = '<p class="loading" style="color: #7f8c8d; margin-top: 12px;">Searching...</p>';
+            resultsDiv.innerHTML = '<p class="loading">Searching...</p>';
 
             // Use a simple client-side search against the asinfo data
             // For now, redirect to AS page if it looks like an ASN
@@ -397,7 +404,7 @@
             }
 
             // Show a message that server-side search is coming
-            resultsDiv.innerHTML = '<p style="color: #7f8c8d; margin-top: 12px; font-size: 13px;">AS name search coming soon. For now, try an AS number.</p>';
+            resultsDiv.innerHTML = '<p class="search-message">AS name search coming soon. For now, try an AS number.</p>';
         });
 
         // IP lookup