feat(tests): add Jest+Supertest infrastructure with jump route suite (14 tests)

- Extract Express app creation into src/createApp.js to enable testing without starting the server
- Add Jest, Supertest, test helpers (createTestApp, auth token generator)
- Write 14 integration tests for skydive/jumps: auth protection, CRUD, ownership checks

Bugs caught and fixed by the test suite:
- MongoDB models: author field typed as Schema.Types.UUID (Mongoose 6 rejects string UUIDs) → changed to String
- Jump.toJSONFor: called toProfileJSONFor on a UUID string → guarded with typeof check
- exceptions.handler: used err.statusCode but express-jwt throws err.status → returns 500 on 401 errors
- Jump.count(query): deprecated Mongoose method was ignoring the filter → replaced with countDocuments
- jumps.routes GET /: $or query included non-schema field "title" stripped by strictQuery, leaving {} (match-all) → replaced with slug/lieu search
- $regex: was passing a JS RegExp object which serializes to {} in MongoDB → now passes raw string

tests/helpers/auth.js

@@ -0,0 +1,19 @@
+const jwt = require('jsonwebtoken');
+
+const TEST_USER_ID = 'a0000000-0000-0000-0000-000000000001';
+const TEST_USERNAME = 'test_user';
+
+function generateToken(userId = TEST_USER_ID, username = TEST_USERNAME) {
+    const secret = process.env.SECRET;
+    const exp = Math.floor(Date.now() / 1000) + 86400;
+    return jwt.sign({ id: userId, username, exp }, secret, { algorithm: 'HS256' });
+}
+
+const mockUser = {
+    id: TEST_USER_ID,
+    username: TEST_USERNAME,
+    email: 'test@example.com',
+    role: 'Admin',
+};
+
+module.exports = { generateToken, mockUser, TEST_USER_ID, TEST_USERNAME };