Polish launch and picker windows

[8damon]

Summary

• fixes global button hover/pressed foregrounds so light hover states keep dark readable text
• softens window and diagnostics borders without pulling in private panes or server UI
• widens and reflows launch parameters to reduce clipping and vertical scrolling
• adds close/clear affordances to the process picker search flow
• removes the unused startup rule-intel block from the welcome window

Fixes #33
Refs #3

Validation

• git diff --check
• denied-string scan for Enterprise-only terms in staged additions
• dotnet build VCXProj/BlackbirdInterface.csproj -c Debug
• started BlackbirdInterface.exe from the Debug output and stopped it after a 5-second startup smoke test