refactor(icons): replace SVG icons with Material Symbols

Replace custom SVG icons with Material Symbols equivalents:
- play.svg → play_arrow icon
- drag-handle.svg → drag_handle icon
- early-on.svg → schedule icon
- estimate-remaining.svg → hourglass_empty icon
- calendar.svg → (unused, removed)
- keep.svg → bookmark_add icon (unpinned state)
- keep-filled.svg → bookmark icon (pinned state)
- bottom-panel-open.svg → (unused, removed)

This reduces custom SVG assets and leverages the Material Symbols font
for consistent icon rendering across the application.

package-lock.json

@@ -15,7 +15,6 @@
         "@capacitor/ios": "^7.4.4",
         "@capacitor/keyboard": "^7.0.4",
         "@capacitor/status-bar": "^7.0.4",
-        "@rollup/rollup-linux-x64-gnu": "4.55.3",
         "electron-dl": "^3.5.2",
         "electron-localshortcut": "^3.2.1",
         "electron-log": "^5.4.3",