Add Memos API adapter and settings UI

Introduce a Memos API adapter to unify compatibility across API flavors (v020-v021, v023, modern) and probe/detect server flavor. Add js/compat/memosApi.adapter.js and rename existing compat modules (memosApi.v024.js -> memosApi.modern.js, memosApi.v1.js -> memosApi.v020-v021.js) and trim probe from v023. Add settings UI support: new i18n keys in en/ja/ko/zh_CN, settings panel styles in css/main.css, new settings input binding and save flow in js (attachment-only default text persisted). Refactor oper.js to use the adapter for uploads, deletes, tag listing, search and image preview auth handling; add helper functions for attachment-only default text and settings payload. Update i18n bindings, popup, manifest and README changelog accordingly.
closed #5

_locales/en/messages.json

@@ -23,6 +23,18 @@
    "supportedMemosVersion": {
       "message": "Compatible with Memos v0.15.0 - 0.27.x"
    },
+   "settingsConnectionTitle": {
+      "message": "Connection"
+   },
+   "settingsConnectionDesc": {
+      "message": "Configure the Memos site URL and access token."
+   },
+   "settingsPostingTitle": {
+      "message": "Posting"
+   },
+   "settingsPostingDesc": {
+      "message": "Default text for attachment-only sends"
+   },
    "placeApiUrl":{
       "message": "Memos site URL"
    },
@@ -50,6 +62,9 @@
    "placeShowInput":{
       "message": "Default 'Everyone can see' Tag name"
    },
+   "placeAttachmentOnlyDefaultText": {
+      "message": "Default text for attachment-only sends (leave blank to use built-in text)"
+   },
    "uploadedListTitle": {
       "message": "Uploaded files, Drag to reorder"
    },