Add updateassets command with webapp code detection

- Add updateassets command to update plugin files from embedded assets
- Only include webapp assets if plugin manifest indicates webapp code presence
- Compare file contents before updating to avoid unnecessary writes
- Display count of updated files in completion message

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/.editorconfig

@@ -0,0 +1,27 @@
+# http://editorconfig.org/
+
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true
+
+[*.go]
+indent_style = tab
+
+[*.{js,jsx,ts,tsx,json,html}]
+indent_style = space
+indent_size = 4
+
+[webapp/package.json]
+indent_size = 2
+
+[{Makefile,*.mk}]
+indent_style = tab
+
+[*.md]
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = false