chore: rename 'Secret Scanner' to 'Auto-redact' in all UI

'Secret Scanner' described what it looks for. 'Auto-redact' describes
what it does — clearer for users. Renamed in popup, options page,
org section, and README. Internal code (secret-scanner.js) unchanged
to avoid breaking references.

https://claude.ai/code/session_01SWSwDfMVij53bCTNSCLMwn

src/options/options.html

@@ -49,8 +49,8 @@
       </div>
       <div class="setting-row">
         <div>
-          <label>Secret scanning</label>
-          <p class="setting-desc">Auto-detect and redact API keys, tokens, passwords, SSNs, credit card numbers</p>
+          <label>Auto-redact secrets</label>
+          <p class="setting-desc">Automatically redact API keys, tokens, passwords, SSNs, credit card numbers</p>
         </div>
         <label class="toggle">
           <input type="checkbox" id="secretScanning" checked>
@@ -361,7 +361,7 @@
     <!-- Organization -->
     <section class="section">
       <h2>Organization</h2>
-      <p class="section-desc">Join an organization to receive required substitution rules and secret scanner patterns from your admin. Org rules merge with your personal rules and cannot be disabled.</p>
+      <p class="section-desc">Join an organization to receive required substitution rules and auto-redact patterns from your admin. Org rules merge with your personal rules and cannot be disabled.</p>
 
       <div id="orgNotJoined">
         <div style="display:flex;gap:8px;flex-wrap:wrap;margin-bottom:8px">