fix: add TypeScript declarations and fix build errors

Fixed TypeScript compilation errors preventing Docker build:

1. Added type declarations for convert-units library:
   - Created types/convert-units.d.ts with proper interfaces
   - Defined Unit and Converter interfaces
   - Made value parameter optional in convert() function
   - Methods like measures() accessible on Converter instance

2. Fixed CommandPalette type error:
   - Added explicit type annotation to commands array
   - Made color property optional (color?: string)
   - Theme commands don't have color, measure commands do

Build now completes successfully:
- TypeScript compilation passes
- Static pages generate correctly
- Ready for Docker build

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

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

components/ui/CommandPalette.tsx

@@ -29,7 +29,14 @@ export default function CommandPalette({
   const inputRef = useRef<HTMLInputElement>(null);
 
   // Commands
-  const commands = [
+  const commands: Array<{
+    id: string;
+    label: string;
+    icon: any;
+    action: () => void;
+    keywords: string[];
+    color?: string;
+  }> = [
     {
       id: 'theme-light',
       label: 'Switch to Light Mode',