Fix Windows binary detection for Bun compiled executables

- Updated isBunBinary detection to check for %7EBUN (URL-encoded ~BUN)
- Simplified build:binary script to remove Unix-specific shell syntax
- Binary now correctly locates supporting files next to executable on Windows

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- **Windows binary detection**: Fixed Bun compiled binary detection on Windows by checking for URL-encoded `%7EBUN` in addition to `$bunfs` and `~BUN` in `import.meta.url`. This ensures the binary correctly locates supporting files (package.json, themes, etc.) next to the executable.
+
 ## [0.12.15] - 2025-12-06
 
 ### Fixed