fix: add missing parent_id and level columns for subtasks support

ROOT CAUSE: During phases 1-5, subtask support was added which requires
parent_id and level columns in note_todos and global_todos tables.
However, the auto-migrate script did not include this migration,
causing 500 errors when the API tried to SELECT these non-existent columns.

Changes:
- scripts/auto-migrate.js: Added Migration 4 to create parent_id and
  level columns if they don't exist

- config/database.js: Updated CREATE TABLE statements to include
  parent_id and level columns in the initial schema

This fixes the 500 error on GET /api/notes that occurred because the
code was trying to SELECT columns that didn't exist in production.

The migration will run automatically on next Docker startup and add
the missing columns without data loss.

Fixes: "je n ai plus aucune note qui s affichent" - notes not displaying

config/database.js

@@ -126,6 +126,8 @@ async function initDatabase() {
         completed BOOLEAN DEFAULT FALSE,
         priority BOOLEAN DEFAULT FALSE,
         position INTEGER DEFAULT 0,
+        parent_id INTEGER REFERENCES note_todos(id) ON DELETE CASCADE,
+        level INTEGER DEFAULT 0,
         created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
         completed_at TIMESTAMP
       )
@@ -140,6 +142,8 @@ async function initDatabase() {
         completed BOOLEAN DEFAULT FALSE,
         priority BOOLEAN DEFAULT FALSE,
         in_progress INTEGER DEFAULT 0,
+        parent_id INTEGER REFERENCES global_todos(id) ON DELETE CASCADE,
+        level INTEGER DEFAULT 0,
         created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
         completed_at TIMESTAMP
       )