feat(core,tooling): Windows support — shell selection, install.ps1, win-x64 release package, Windows CI (#79)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.gitattributes

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+# Normalize text files to LF in the repo AND in the working tree (eol=lf beats core.autocrlf),
+# so a Windows checkout matches what Prettier's endOfLine=lf expects and shell scripts stay
+# runnable under Git-Bash.
+* text=auto eol=lf
+
+# Shell scripts must be LF (a CRLF shebang line breaks the interpreter).
+*.sh text eol=lf
+
+# PowerShell is the one Windows-native text format we ship; keep it CRLF for notepad/PS 5.1
+# friendliness (PowerShell itself accepts both).
+*.ps1 text eol=crlf
+
+# Binary assets: never subject to text normalization or diffs.
+*.png binary
+*.webp binary