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.

js/i18n.js

@@ -86,6 +86,7 @@ function applyStaticI18n() {
 	setText('lockPublic', 'lockPublic')
 
 	setText('content_submit_text', 'submitBtn')
+	setText('fullscreen', 'fullscreenBtn')
 
 	setPlaceholder('hideInput', 'placeHideInput')
 	setPlaceholder('showInput', 'placeShowInput')
@@ -111,6 +112,8 @@ function applyStaticI18n() {
 	setTitle('search', 'tipSearch')
 	setTitle('lock', 'tipVisibility')
 	setTitle('content_submit_text', 'tipSend')
+	setTitle('fullscreen', 'tipFullscreen')
+	setTitle('editor-resize-handle', 'tipResize')
 }
 
 async function setUiLanguage(nextLang, { persist = true } = {}) {