chore: rework plugin readmes, json changelogs and standalone repo setup

plugins/file-manager/CONTRIBUTING.md

@@ -0,0 +1,28 @@
+# Contributing to File Manager
+
+## Development
+
+```bash
+npm run build      # build into dist/
+npm run test       # run this plugin's tests
+npm run typecheck  # type-check this plugin
+npm run validate   # check manifest.json
+npm run format     # format the code with Prettier
+```
+
+## Settings
+
+### User
+
+- **Simultaneous File Transfers:** how many uploads and downloads run at once
+- **Confirm before moving files to trash:** ask before a delete. Permanent deletes always ask
+
+### Host
+
+- **Enable File Manager:** show the file manager for this host
+- **Default Path:** the folder to open first
+- **SCP Legacy Mode:** use SCP for hosts without a working SFTP server
+
+## Permissions
+
+- `file-manager.use`: browse, edit and transfer files. Admins and users have it by default.