Fix Order Entry connect + back arrows

- frontend.py: /book was calling /book on matcher (404); fixed to
/orderbook/<symbol> with ?symbol= query param
- Order Entry: pass selected symbol to /book, reload on symbol change
- Order Entry: add ← Dashboard link via onclick (not href)
- FIX UI: ← Dashboard href="/" was rewritten by nginx sub_filter to
/fix/; fixed by switching to onclick so sub_filter can't touch it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fix-ui-client/templates/index.html

@@ -132,7 +132,7 @@
       <span class="dot"></span>
       <span id="status-text">Connecting...</span>
     </span>
-    <a href="/" style="margin-left:auto; padding:4px 14px; background:#6c757d; color:#fff; border-radius:20px; font-size:12px; font-weight:bold; text-decoration:none;">← Dashboard</a>
+    <a onclick="window.location.href='/'" style="margin-left:auto; padding:4px 14px; background:#6c757d; color:#fff; border-radius:20px; font-size:12px; font-weight:bold; text-decoration:none; cursor:pointer;">← Dashboard</a>
   </h1>
 
   <div class="container">

frontend/frontend.py

@@ -77,7 +77,10 @@ def securities():
 @app.route('/book')
 def book():
     import requests
-    r = requests.get(f"{Config.MATCHER_URL}/book", timeout=2)
+    symbol = request.args.get('symbol', '')
+    if not symbol:
+        return jsonify({"bids": [], "asks": []})
+    r = requests.get(f"{Config.MATCHER_URL}/orderbook/{symbol}", timeout=3)
     return (r.text, r.status_code, {'Content-Type': 'application/json'})
 
 @app.route('/trades')

frontend/templates/index.html

@@ -124,6 +124,7 @@
       <span id="status-text">Connecting...</span>
     </span>
     <button id="reconnect-btn" class="btn-reconnect" onclick="reconnect()">Reconnect</button>
+    <a onclick="window.location.href='/'" style="margin-left:auto; padding:4px 14px; background:#6c757d; color:#fff; border-radius:20px; font-size:12px; font-weight:bold; text-decoration:none; cursor:pointer;">← Dashboard</a>
   </h1>
 
   <!-- Order Entry -->
@@ -137,7 +138,7 @@
         </div>
         <div class="form-group">
           <label>Symbol</label>
-          <select id="symbol-select" name="symbol">
+          <select id="symbol-select" name="symbol" onchange="loadBook()">
             <option value="">Loading...</option>
           </select>
         </div>
@@ -326,8 +327,9 @@
 
     async function loadBook() {
       const now = new Date().toLocaleTimeString();
+      const symbol = document.getElementById('symbol-select')?.value || '';
       try {
-        const r = await fetch(BASE + '/book');
+        const r = await fetch(BASE + '/book?symbol=' + encodeURIComponent(symbol));
         const b = await r.json();
         renderBook(b);
         document.getElementById('book-updated').textContent = 'Updated: ' + now;