Fix extension icons and AMPP autofill

- Generate missing chrome-extension/images/ icons (16, 48, 128px)
  that were absent from repo, causing 'Could not load manifest' error
- Fix AMPP API key field: add readonly+onfocus to block Bitwarden/browser autofill

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

public/index.html

@@ -571,7 +571,7 @@ body::before{content:'';position:fixed;inset:0;background:radial-gradient(ellips
       </div>
       <div class="form-group">
         <label class="form-label">API Key (Base64 credentials)</label>
-        <input class="form-input" id="ampp-api-key" type="password" placeholder="Leave blank to keep existing" autocomplete="new-password"/>
+        <input class="form-input" id="ampp-api-key" type="password" placeholder="Enter API key — leave blank to keep existing" autocomplete="off" readonly onfocus="this.removeAttribute('readonly')"/>
         <div class="form-hint" id="ampp-key-hint"></div>
       </div>
       <div class="btn-row">