test: improve test infrastructure and fix test assertions

- Add mockPapaParse helper to centralize CSV mocking
- Fix test assertions to match actual output (German month names)
- Add missing DOM elements to test setup (projectFile, csvFile, etc.)
- Update vitest to v4.0.14 for improved testing capabilities
- Make setupEventHandlers globally accessible for testing
- Use textContent instead of innerText for better consistency
- Fix autoLoadDefaultProject test to check all three fallback paths
- Add proper event handler setup in integration tests
- Improve error handling test assertions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

engine.js

@@ -183,8 +183,8 @@ window.timelineEngine = {
   async loadProjectConfigObject(cfg) {
     this.config = cfg;
     const name = cfg.name || "Timeline";
-    document.getElementById("projectName").innerText = name;
-    document.getElementById("projectSubtitle").innerText =
+    document.getElementById("projectName").textContent = name;
+    document.getElementById("projectSubtitle").textContent =
       cfg.description || "Projektkonfiguration geladen.";
 
     // Update project status
@@ -531,7 +531,7 @@ window.svgViewer = {
 
 // --------- UI event handlers ---------
 
-function setupEventHandlers() {
+window.setupEventHandlers = function() {
   const projectInput = document.getElementById("projectInput");
   if (projectInput) {
     projectInput.addEventListener("change", async (ev) => {