fix(code): reduce window minWidth from 1200 to 800

[thmsobrmlr]

Summary

• The main BrowserWindow enforced a minWidth: 1200, preventing users on common laptop displays (e.g. 1440–1600px wide) from tiling the app to half a screen.
• Drop the floor to 800px. minHeight: 600 is unchanged — already low enough.
• No other constraints fight this: no root-level CSS min-width, and internal min-w-* usages are scoped to components that already handle narrower widths.

Test plan

• pnpm dev:code and drag the window inward; confirm it now resizes down to ~800px wide
• Tile the window to half a 1600px display; confirm tiling succeeds
• Sanity-check the header, sidebar, and task detail panels at ~800px for clipping

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(code): reduce window minWidth so hal..." | Re-trigger Greptile}