fix: extension loading in Bun binary (#681)

- Remove loader exports from index.ts to break circular dependency
- Static import of index.js in loader.ts for virtualModules
- Add @mariozechner/pi-agent-core to virtualModules
- Update @mariozechner/jiti to 2.6.5 (bundles babel for Bun binary)
- Update SDK docs to use correct extension terminology

package-lock.json

@@ -13,6 +13,7 @@
 				"packages/coding-agent/examples/extensions/with-deps"
 			],
 			"dependencies": {
+				"@mariozechner/jiti": "^2.6.5",
 				"@mariozechner/pi-coding-agent": "^0.30.2",
 				"get-east-asian-width": "^1.4.0"
 			},
@@ -1781,9 +1782,9 @@
 			}
 		},
 		"node_modules/@mariozechner/jiti": {
-			"version": "2.6.2",
-			"resolved": "https://registry.npmjs.org/@mariozechner/jiti/-/jiti-2.6.2.tgz",
-			"integrity": "sha512-CcFowm/fDWcEMH/F47DQcdawpLQb0nw+WR+hZOv8mgAeACFJxE9uo3cXjUk/5Cl3j23t/oxvtxxUtlBCUIGeQg==",
+			"version": "2.6.5",
+			"resolved": "https://registry.npmjs.org/@mariozechner/jiti/-/jiti-2.6.5.tgz",
+			"integrity": "sha512-faGUlTcXka5l7rv0lP3K3vGW/ejRuOS24RR2aSFWREUQqzjgdsuWNo/IiPqL3kWRGt6Ahl2+qcDAwtdeWeuGUw==",
 			"license": "MIT",
 			"dependencies": {
 				"std-env": "^3.10.0",