fix: regenerate icons with bold M for taskbar visibility

Regenerated all app icons using the generate-icons script to ensure
small sizes (≤64px) use appicon-small.svg with bold stroke-width=2.4
for the "M" logo. This makes the McpMux icon clearly visible in Windows
taskbar and other small contexts.

The script automatically:
- Uses appicon-small.svg for sizes ≤64px (taskbar/tray icons)
- Uses appicon-512.svg for larger sizes (full detail)
- Generates multi-resolution icon.ico with all required sizes

Fixes icon visibility issue where the "M" was too thin in taskbar.

Signed-off-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: its-mash