stale-check compared LastWriteTime against a stamp file that does not
exist yet on the first build, so Get-Item threw PathNotFound and aborted
the build before make DSK.
- build.ps1: guard the texSrc/texStamp mtime comparison with
Test-Path $TexStamp; $needTex is already $true when the stamp is
absent, so the comparison is only meaningful when both files exist
- .gitignore: ignore IDEA.md local scratch note
Verified: .\build.bat now reaches gen_textures.py and emits
back.rgba / startMenuLogo.rgba / bootlogo.rgba into
SYSTEM/system/deshab64/desktop/textures/.
boonxiong2