refactor: Standardize data processing and update to Svelte 5 runes

This commit introduces a major refactoring of the data processing logic across multiple modules (events, archives, posts, sponsorships) to use a standardized pattern with . This improves consistency and maintainability.

Key changes:
- Replaced module-specific data processing with a generic helper.
- Removed deprecated  functions.
- Updated Svelte components to leverage the new Svelte 5 runes, simplifying state management.
- Fixed linting errors and updated test configurations.
- Added .

test-results/.last-run.json

@@ -1,4 +1,4 @@
 {
-  "status": "interrupted",
+  "status": "failed",
   "failedTests": []
 }