fix(#453): replace HEREDOC with literal newlines for Windows compatibility

- git tag command in complete-milestone.md used HEREDOC syntax
- HEREDOC fails silently on Windows Git Bash
- Literal newlines in quoted strings work cross-platform

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

get-shit-done/workflows/complete-milestone.md

@@ -534,8 +534,7 @@ fi
 Create git tag:
 
 ```bash
-git tag -a v[X.Y] -m "$(cat <<'EOF'
-v[X.Y] [Name]
+git tag -a v[X.Y] -m "v[X.Y] [Name]
 
 Delivered: [One sentence]
 
@@ -544,9 +543,7 @@ Key accomplishments:
 - [Item 2]
 - [Item 3]
 
-See .planning/MILESTONES.md for full details.
-EOF
-)"
+See .planning/MILESTONES.md for full details."
 ```
 
 Confirm: "Tagged: v[X.Y]"