Migrate the API to native ESM and vitest; pin Node 26

Prep PR for the admin auth module (docs/plan-admin-auth.md step 1).
better-auth 1.7 ships ESM only, so the API moves off CommonJS:

- "type": "module", module nodenext, target ES2024, .js suffixes on all
  relative imports, require('mariadb'|'cors') replaced by imports, and
  export= packages (winston, app-root-path, bcrypt) consumed via default
  imports. The logger now uses appRoot.path explicitly.
- TypeScript 5.9, @types/node 26, tslint removed. Node 26 pinned via
  engines and .nvmrc (Plesk runs 26).
- Jest 28 + ts-jest replaced by vitest 5. Eight test files depend on
  hoisted module mocks with static imports and resetModules + require,
  which Jest's ESM mode does not support; vitest keeps them nearly
  verbatim. Coverage via @vitest/coverage-v8 (lcov), Sonar generic report
  via vitest-sonar-reporter, so sonar-project.properties is unchanged.
  vitest.config.ts sets FEEDBACK_IP_SALT so the suite passes without a
  local .env.
- dotenv 8 -> 16 and axios 0.24 -> 1.x: their old typings are not
  resolvable under nodenext.
- autoCommit: false dropped from the pool configs; it is not a mariadb
  connector option and was silently ignored.

tsc clean, 96/96 tests green, compiled app boots and serves /, /docs and
CORS under Node ESM.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/models/calendar/Calendar.db.ts

@@ -1,6 +1,5 @@
 import * as dotenv from 'dotenv';
-
-const mariadb = require('mariadb');
+import mariadb from 'mariadb';
 
 dotenv.config();
 
@@ -10,8 +9,7 @@ export namespace NachklangCalendarDB {
 		user: process.env.DB_USER,
 		password: process.env.DB_PASSWORD,
 		database: process.env.CALENDAR_DB,
-		connectionLimit: 5,
-		autoCommit: false
+		connectionLimit: 5
 	});
 
 	export const getConnection = async () => {

src/models/calendar/Calendar.router.ts

@@ -3,9 +3,9 @@
  */
 import express, {Request, Response} from 'express';
 import {Guid} from 'guid-typescript';
-import logger from '../../middleware/logger';
-import {eventsRouter} from './events/events.router';
-import {usersRouter} from './users/users.router';
+import logger from '../../middleware/logger.js';
+import {eventsRouter} from './events/events.router.js';
+import {usersRouter} from './users/users.router.js';
 
 /**
  * Router Definition

src/models/calendar/events/credentials.service.ts

@@ -1,5 +1,5 @@
 import * as dotenv from 'dotenv';
-import * as UserService from '../users/users.service';
+import * as UserService from '../users/users.service.js';
 
 
 dotenv.config();

src/models/calendar/events/events.router.ts

@@ -3,13 +3,13 @@
  */
 
 import express, {Request, Response} from 'express';
-import {Event} from './event.interface';
-import * as EventService from './events.service';
-import * as iCalService from './icalgenerator.service';
-import * as CredentialService from './credentials.service';
-import * as UserService from '../users/users.service';
+import {Event} from './event.interface.js';
+import * as EventService from './events.service.js';
+import * as iCalService from './icalgenerator.service.js';
+import * as CredentialService from './credentials.service.js';
+import * as UserService from '../users/users.service.js';
 import {Guid} from 'guid-typescript';
-import logger from '../../../middleware/logger';
+import logger from '../../../middleware/logger.js';
 
 
 /**

src/models/calendar/events/events.service.ts

@@ -1,7 +1,7 @@
 import * as dotenv from 'dotenv';
 import {Guid} from 'guid-typescript';
-import {Event} from './event.interface';
-import {NachklangCalendarDB} from '../Calendar.db';
+import {Event} from './event.interface.js';
+import {NachklangCalendarDB} from '../Calendar.db.js';
 
 
 dotenv.config();

src/models/calendar/events/icalgenerator.service.ts

@@ -1,4 +1,4 @@
-import {Event} from './event.interface';
+import {Event} from './event.interface.js';
 
 /**
  * Interface to external classes - Turns the given events into an ical string

src/models/calendar/users/users.router.ts

@@ -3,11 +3,11 @@
  */
 
 import express, {Request, Response} from 'express';
-import * as UserService from './users.service';
-import {Session} from './session.interface';
-import {User} from './user.interface';
+import * as UserService from './users.service.js';
+import {Session} from './session.interface.js';
+import {User} from './user.interface.js';
 import {Guid} from 'guid-typescript';
-import logger from '../../../middleware/logger';
+import logger from '../../../middleware/logger.js';
 
 /**
  * Router Definition

src/models/calendar/users/users.service.ts

@@ -1,10 +1,10 @@
 import * as dotenv from 'dotenv';
-import * as bcrypt from 'bcrypt';
+import bcrypt from 'bcrypt';
 import {Guid} from 'guid-typescript';
-import {User} from './user.interface';
-import {Session} from './session.interface';
-import {NachklangCalendarDB} from '../Calendar.db';
-import {MailService} from "../../../common/common.mail";
+import {User} from './user.interface.js';
+import {Session} from './session.interface.js';
+import {NachklangCalendarDB} from '../Calendar.db.js';
+import {MailService} from '../../../common/common.mail.js';
 
 dotenv.config();