Qualify themes, native app icons and palette layout

Qualify Launchpad's System, Light and Dark appearances with real macOS app icons and consistent window geometry.

Acceptance:

• Palette has a visible outer border and rounded clipping.
• Search, tabs, result rows, clipboard preview and footer keep a consistent height.
• Command editor and Settings preserve fixed action footers with scrollable content.
• Real icons are read through Craft's NSWorkspace integration, with a normal icon fallback.
• Both appearances have readable inputs, selected rows, errors and keyboard focus.
• Capture genuine native screenshots for the Store listing.

Implemented in 1d0b548. Signed sandbox qualification used Launchpad 0.1.2 (Build 11), a public-API Craft runtime, visible rounded window borders, consistent scroll regions and fixed action footers. Real macOS application icons and original Pantry logos render in the native window. Genuine 1440 x 900 screenshots of Dark, Light, calculator, GitHub and Pantry are committed for the Store listing. Final version delivery and Apple review remain tracked separately in #6.