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/replace_formatters.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""
+Script to replace inline formatCurrency functions with shared formatter utilities
+"""
+
+import re
+import sys
+
+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
+
+        # Check if already has the import
+        has_formatter_import = 'from \'$lib/utils/formatters\'' in content or 'from "$lib/utils/formatters"' in content
+
+        # Find the <script> tag
+        script_match = re.search(r'(<script[^>]*>)', content)
+        if not script_match:
+            print(f"  ⚠️  No <script> tag found")
+            return False
+
+        # Add import if not present
+        if not has_formatter_import:
+            script_tag = script_match.group(1)
+            # Find where to insert (after <script> tag)
+            script_end = script_match.end()
+
+            # Get existing imports to find the right place
+            imports_section_match = re.search(r'<script[^>]*>(.*?)(?:\n\n|\n  export|\n  let)', content, re.DOTALL)
+            if imports_section_match:
+                imports_end = imports_section_match.end() - len(imports_section_match.group(0).split('\n')[-1])
+                insert_pos = imports_end
+            else:
+                insert_pos = script_end
+
+            new_import = "\n  import { formatCurrency } from '$lib/utils/formatters';"
+            content = content[:insert_pos] + new_import + content[insert_pos:]
+            print(f"  ✓ Added import")
+
+        # Remove the formatCurrency function definition
+        # Pattern for the function with different variations
+        patterns = [
+            r'\n  function formatCurrency\(amount\) \{\n    return new Intl\.NumberFormat\(\'de-CH\',\s*\{\n\s*style:\s*\'currency\',\n\s*currency:\s*\'CHF\'\n\s*\}\)\.format\(amount\);\n  \}',
+            r'\n  function formatCurrency\(amount,\s*currency\s*=\s*\'CHF\'\) \{\n    return new Intl\.NumberFormat\(\'de-CH\',\s*\{\n\s*style:\s*\'currency\',\n\s*currency:\s*currency\n\s*\}\)\.format\(amount\);\n  \}',
+        ]
+
+        for pattern in patterns:
+            if re.search(pattern, content):
+                content = re.sub(pattern, '', content)
+                print(f"  ✓ Removed formatCurrency function")
+                break
+
+        # Check if content changed
+        if content != original_content:
+            with open(filepath, 'w', encoding='utf-8') as f:
+                f.write(content)
+            print(f"  ✅ Updated successfully")
+            return True
+        else:
+            print(f"  ⚠️  No changes needed")
+            return False
+
+    except Exception as e:
+        print(f"  ❌ Error: {e}")
+        return False
+
+def main():
+    print("=" * 60)
+    print("Replacing formatCurrency functions with shared utilities")
+    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()