feat(coding-agent): configurable app name and config dir for forks (#95)

- Add piConfig to package.json for app name and config directory
- Consolidate paths.ts into config.ts with clearer naming
- Fix Bun binary detection (changed from %7EBUN to $bunfs)
- Update all hardcoded paths to use config.ts exports
- getThemesDir() for built-in themes, getCustomThemesDir() for user themes

packages/coding-agent/package.json

@@ -3,6 +3,10 @@
 	"version": "0.12.4",
 	"description": "Coding agent CLI with read, bash, edit, write tools and session management",
 	"type": "module",
+	"piConfig": {
+		"name": "pi",
+		"configDir": ".pi"
+	},
 	"bin": {
 		"pi": "dist/cli.js"
 	},