fix: correct keyboard shortcut modifier matching logic

The previous implementation had inverted logic that prevented keyboard
shortcuts from working. The check `shortcut.ctrl ? event.ctrlKey : !event.ctrlKey`
meant that if ctrl wasn't specified, it required ctrl to NOT be pressed,
which broke shortcuts with only meta keys.

**Changes:**
- Fix modifier matching: only check modifiers that are explicitly required (=== true)
- Add check to prevent unwanted modifiers (e.g., if only meta+c, reject ctrl+meta+c)
- Improve cross-platform meta/cmd key handling (Mac uses metaKey, Windows/Linux uses ctrlKey)
- Allow meta key to permit ctrl on non-Mac platforms (meta is treated as ctrl equivalent)

**Now working shortcuts in playground:**
- Cmd/Ctrl+C: Copy color to clipboard
- Cmd/Ctrl+S: Share color (copy URL)
- Cmd/Ctrl+R: Generate random color

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

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

lib/hooks/useKeyboard.ts

@@ -36,22 +36,37 @@ export function useKeyboard(shortcuts: KeyboardShortcut[]) {
     const handleKeyDown = (event: KeyboardEvent) => {
       for (const shortcut of shortcuts) {
         const keyMatches = event.key.toLowerCase() === shortcut.key.toLowerCase();
-        const ctrlMatches = shortcut.ctrl ? event.ctrlKey : !event.ctrlKey;
-        const shiftMatches = shortcut.shift ? event.shiftKey : !event.shiftKey;
-        const altMatches = shortcut.alt ? event.altKey : !event.altKey;
-        const metaMatches = shortcut.meta ? event.metaKey : !event.metaKey;
 
-        // On Windows/Linux, treat meta as ctrl for convenience
-        const modifierMatches = shortcut.meta
-          ? event.metaKey || (event.ctrlKey && !navigator.platform.includes('Mac'))
-          : metaMatches;
+        // Check if required modifiers match (only check if explicitly required)
+        const ctrlMatches = shortcut.ctrl === true ? event.ctrlKey : true;
+        const shiftMatches = shortcut.shift === true ? event.shiftKey : true;
+        const altMatches = shortcut.alt === true ? event.altKey : true;
+
+        // Handle meta/cmd key with cross-platform support
+        let metaMatches = true;
+        if (shortcut.meta === true) {
+          // On Mac: require Cmd key
+          // On Windows/Linux: accept Ctrl key as Cmd equivalent
+          const isMac = navigator.platform.includes('Mac');
+          metaMatches = isMac ? event.metaKey : event.ctrlKey;
+        }
+
+        // Ensure unwanted modifiers are not pressed (unless explicitly required)
+        const noExtraCtrl = shortcut.ctrl === true || shortcut.meta === true || !event.ctrlKey;
+        const noExtraShift = shortcut.shift === true || !event.shiftKey;
+        const noExtraAlt = shortcut.alt === true || !event.altKey;
+        const noExtraMeta = shortcut.meta === true || !event.metaKey;
 
         if (
           keyMatches &&
           ctrlMatches &&
           shiftMatches &&
           altMatches &&
-          modifierMatches
+          metaMatches &&
+          noExtraCtrl &&
+          noExtraShift &&
+          noExtraAlt &&
+          noExtraMeta
         ) {
           event.preventDefault();
           shortcut.handler(event);