add general file upload support with pool-aware tus client

- add "uploadFile" i18n key (en, zh-CN, zh-TW)
- introduce putFileToPool for tus upload with X-FilePool header
- add ComposeLogic.pickGeneralFile for arbitrary files
- extend uploadAttachment to support poolId override
- add toolbar button for general file upload

Signed-off-by: Texas0295 <kimura@texas0295.top>

assets/i18n/en-US.json

@@ -168,6 +168,7 @@
   "addPhoto": "Add photo",
   "addAudio": "Add audio",
   "addFile": "Add file",
+  "uploadFile": "Upload File",
   "recordAudio": "Record Audio",
   "linkAttachment": "Link Attachment",
   "fileIdCannotBeEmpty": "File ID cannot be empty",