refactor: rename index.ts to action.ts (#408)

action.yml

@@ -34,4 +34,4 @@ outputs:
     value: ${{ steps.process-inputs.outputs.build-dir }}
 runs:
   using: node20
-  main: dist/index.mjs
+  main: dist/action.mjs

rollup.config.js

@@ -2,7 +2,7 @@ import { nodeResolve } from "@rollup/plugin-node-resolve";
 import typescript from "@rollup/plugin-typescript";
 
 export default {
-  input: "src/index.ts",
+  input: "src/action.ts",
   output: {
     dir: "dist",
     entryFileNames: "[name].mjs",