refactor: consolidate formatting utilities and add testing infrastructure

- Replace 8 duplicate formatCurrency functions with shared utility
- Add comprehensive formatter utilities (currency, date, number, etc.)
- Set up Vitest for unit testing with 38 passing tests
- Set up Playwright for E2E testing
- Consolidate database connection to single source (src/utils/db.ts)
- Add auth middleware helpers to reduce code duplication
- Fix display bug: remove spurious minus sign in recent activity amounts
- Add path aliases for cleaner imports ($utils, $models)
- Add project documentation (CODEMAP.md, REFACTORING_PLAN.md)

Test coverage: 38 unit tests passing
Build: successful with no breaking changes

scripts/update_formatter_calls.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+"""
+Script to update formatCurrency calls to include CHF and de-CH parameters
+"""
+
+import re
+
+files_to_update = [
+    "/home/alex/.local/src/homepage/src/routes/cospend/+page.svelte",
+    "/home/alex/.local/src/homepage/src/routes/cospend/payments/+page.svelte",
+    "/home/alex/.local/src/homepage/src/routes/cospend/payments/view/[id]/+page.svelte",
+    "/home/alex/.local/src/homepage/src/routes/cospend/recurring/+page.svelte",
+    "/home/alex/.local/src/homepage/src/routes/cospend/settle/+page.svelte",
+]
+
+def process_file(filepath):
+    print(f"Processing: {filepath}")
+
+    try:
+        with open(filepath, 'r', encoding='utf-8') as f:
+            content = f.read()
+
+        original_content = content
+        changes = 0
+
+        # Pattern 1: formatCurrency(amount) -> formatCurrency(amount, 'CHF', 'de-CH')
+        # But skip if already has parameters
+        def replace_single_param(match):
+            amount = match.group(1)
+            # Check if amount already contains currency parameter (contains comma followed by quote)
+            if ", '" in amount or ', "' in amount:
+                return match.group(0)  # Already has parameters, skip
+            return f"formatCurrency({amount}, 'CHF', 'de-CH')"
+
+        content, count1 = re.subn(
+            r'formatCurrency\(([^)]+)\)',
+            replace_single_param,
+            content
+        )
+        changes += count1
+
+        if changes > 0:
+            with open(filepath, 'w', encoding='utf-8') as f:
+                f.write(content)
+            print(f"  ✅ Updated {changes} formatCurrency calls")
+            return True
+        else:
+            print(f"  ⚠️  No changes needed")
+            return False
+
+    except Exception as e:
+        print(f"  ❌ Error: {e}")
+        import traceback
+        traceback.print_exc()
+        return False
+
+def main():
+    print("=" * 60)
+    print("Updating formatCurrency calls with CHF and de-CH params")
+    print("=" * 60)
+
+    success_count = 0
+    for filepath in files_to_update:
+        if process_file(filepath):
+            success_count += 1
+        print()
+
+    print("=" * 60)
+    print(f"Summary: {success_count}/{len(files_to_update)} files updated")
+    print("=" * 60)
+
+if __name__ == "__main__":
+    main()