feat: Options tab in popup + Safari build script

Popup:
- Added 5th "Options" tab with key settings accessible without
  opening the full options page: secret scanning, auto-detect PPI,
  auto-redact, show highlights, document scan preview
- "Open Full Options Page" button for sync/encryption/org/import
- Settings changes in popup immediately broadcast to content scripts

Safari:
- Added build-safari.sh that uses Apple's safari-web-extension-converter
  to generate an Xcode project from the Firefox build
- browser-polyfill.js already handles Safari (uses browser.* like Firefox)

https://claude.ai/code/session_01SWSwDfMVij53bCTNSCLMwn

src/popup/popup.css

@@ -623,6 +623,35 @@ body {
   font-size: 12px;
 }
 
+/* Options tab */
+.setting-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 8px 0;
+  border-bottom: 1px solid #f3f4f6;
+}
+
+.setting-item:last-of-type { border-bottom: none; }
+
+.setting-label {
+  flex: 1;
+  min-width: 0;
+}
+
+.setting-label strong {
+  font-size: 12px;
+  display: block;
+  color: #1f2937;
+}
+
+.setting-label .setting-desc {
+  font-size: 10px;
+  color: #9ca3af;
+  display: block;
+  margin-top: 1px;
+}
+
 /* Footer */
 .footer {
   padding: 8px 16px;