Add fullscreen editor and proportional resize

Introduce a fullscreen editor mode and a proportional resize handle for the memo editor. Updates include:

- UI: add fullscreen button and resize handle to popup.html and related i18n keys for en/ja/ko/zh_CN.
- CSS: styles for .memo-editor, fullscreen state, and #editor-resize-handle, plus layout tweaks for fullscreen.
- Background: enhance context menu handler to retrieve selection text from the active tab using chrome.scripting.executeScript, support opening the extension popup programmatically (tryOpenActionPopup), and factor appendContent logic.
- Oper: implement isFullscreenMode(), openFullscreenTab(), proportional editor resize logic with pointer events (initProportionalEditorResize), focus handling adjustments, and init call. Added helper focusTextareaToEnd().
- Manifest: request scripting and windows permissions required for selection injection and window focus.

These changes enable sending accurate selection text from web pages, allow users to open a fullscreen editor tab, and provide a draggable, proportional resize experience in the popup editor.

_locales/en/messages.json

@@ -163,5 +163,14 @@
    },
    "langKorean": {
       "message": "한국어"
+   },
+   "fullscreenBtn": {
+      "message": "Fullscreen"
+   },
+   "tipFullscreen": {
+      "message": "Open fullscreen editor"
+   },
+   "tipResize": {
+      "message": "Drag to resize (min: default size)"
    }
 }