refactor: restructure to monorepo with backends and apiTest

- Move web/backend to backends/potter-api
- Move web/frontend to backends/potter-api/frontend
- Add root package.json with npm workspaces
- Update README.md with monorepo navigation
- Update .github/workflows/api-tests.yml for dynamic test discovery
- Update bruno_test_scenario.md paths
- Fix .gitignore to allow JSON data files
- Add three new AI tests in apiTest/PotterAPI/AI/

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

backends/potter-api/middleware/spellMiddleware.js

@@ -0,0 +1,9 @@
+let spells = require('../controllers/spellsController.js')
+
+exports.spell_not_found = function (req, res, next) {
+    let result = spells.find(spell => spell._id == req.params.spellId);
+    if (typeof result == 'undefined') {
+        return res.status(404).send({ message: "Spell not found" });
+    }
+    next();
+}