Disable Player module to prevent crashes (external dependency violation)

Issue:
- Player module was crashing when accessed
- Uses external tools (MPV, VLC, FFplay) which violates VideoTools' core principle
- Everything should be internal and lightweight, no external dependencies

Fix:
- Disabled Player module in main menu
- Module still exists in code but is not accessible to users
- Prevents crash by preventing access to broken functionality

Future work needed:
- Implement pure-Go internal player using FFmpeg libraries
- OR implement simple preview-only playback using existing preview system
- Must be self-contained and lightweight

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

main.go

@@ -1618,7 +1618,7 @@ func (s *appState) showMainMenu() {
 			Label:    m.Label,
 			Color:    m.Color,
 			Category: m.Category,
-			Enabled:  m.ID == "convert" || m.ID == "compare" || m.ID == "inspect" || m.ID == "merge" || m.ID == "thumb" || m.ID == "player" || m.ID == "filters" || m.ID == "upscale" || m.ID == "author" || m.ID == "subtitles" || m.ID == "rip", // Enabled modules
+			Enabled:  m.ID == "convert" || m.ID == "compare" || m.ID == "inspect" || m.ID == "merge" || m.ID == "thumb" || m.ID == "filters" || m.ID == "upscale" || m.ID == "author" || m.ID == "subtitles" || m.ID == "rip", // Enabled modules (player disabled - requires internal implementation)
 		})
 	}