docs: add editorconfig setup and remove completed task

- Add EditorConfig section to CONTRIBUTING.md with IDE plugins table
- Remove Issue #28 from Tasks.md (pre-commit hooks now documented)

CONTRIBUTING.md

@@ -24,7 +24,18 @@ make up
 
 Backend: http://127.0.0.1:8000 · Frontend (Vite proxy): http://127.0.0.1:5173
 
-### 3 — Pre-commit hooks
+### 3 — Editor Setup
+
+Install **EditorConfig** plugin for your IDE. Ensures consistent formatting (indent style, line endings) across all editors.
+
+| IDE | Plugin |
+|-----|--------|
+| VS Code | EditorConfig (ms-vscode.editorconfig) |
+| PyCharm / IntelliJ | Built-in (enable in Settings → Editor → Code Style) |
+| Vim / Neovim | editorconfig-vim |
+| Sublime Text | EditorConfig |
+
+### 4 — Pre-commit hooks
 
 **Backend** (pre-commit, all languages):