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

build-safari.sh

@@ -0,0 +1,66 @@
+#!/bin/bash
+#
+# Convert Silent Send for Safari using Apple's safari-web-extension-converter.
+#
+# Prerequisites:
+#   - macOS with Xcode installed (free from Mac App Store)
+#   - Apple Developer account ($99/year) for App Store distribution
+#   - Xcode Command Line Tools: xcode-select --install
+#
+# This script:
+#   1. Builds the Firefox variant (Safari uses browser.* API like Firefox)
+#   2. Runs safari-web-extension-converter to generate an Xcode project
+#   3. The Xcode project can then be built, tested, and submitted to App Store
+#
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+OUT_DIR="$SCRIPT_DIR/safari-build"
+
+# Check for Xcode
+if ! command -v xcrun &> /dev/null; then
+  echo "Error: Xcode is required. Install from the Mac App Store."
+  echo "Then run: xcode-select --install"
+  exit 1
+fi
+
+if ! xcrun --find safari-web-extension-converter &> /dev/null; then
+  echo "Error: safari-web-extension-converter not found."
+  echo "Make sure Xcode is installed and up to date."
+  exit 1
+fi
+
+# Build the Firefox variant (Safari uses browser.* API)
+echo "Building extension..."
+"$SCRIPT_DIR/build.sh" firefox
+
+echo ""
+echo "Converting for Safari..."
+
+# Remove previous build
+rm -rf "$OUT_DIR"
+
+# Convert — generates an Xcode project
+xcrun safari-web-extension-converter \
+  "$SCRIPT_DIR/dist/firefox" \
+  --project-location "$OUT_DIR" \
+  --app-name "Silent Send" \
+  --bundle-identifier "com.silentsend.extension" \
+  --swift \
+  --macos-only \
+  --no-open
+
+echo ""
+echo "Safari project created at: $OUT_DIR"
+echo ""
+echo "Next steps:"
+echo "  1. Open $OUT_DIR/Silent Send.xcodeproj in Xcode"
+echo "  2. Select your Apple Developer Team in Signing & Capabilities"
+echo "  3. Build and run (Cmd+R) to test in Safari"
+echo "  4. To distribute: Product → Archive → Distribute App"
+echo ""
+echo "For App Store submission, you'll also need:"
+echo "  - App Store screenshots (1280x800 for Mac)"
+echo "  - Privacy policy URL"
+echo "  - App description and keywords"