refactor(actions): simplify action path structure

- Relocates action files to a flat directory structure
- Updates references to the new paths for better organization

.gitea/actions/with-post-step/action.yml

@@ -1,11 +0,0 @@
-name: "with-post-step"
-description: "Runs a main command and, afterwards, a post command."
-inputs:
-  main: { description: "Command for the main step", required: true }
-  post: { description: "Command for the post step", required: true }
-  key: { description: "State key", default: POST }
-
-runs:
-  using: node20
-  main: main.js
-  post: main.js

.gitea/actions/with-post-step/main.js

@@ -1,18 +0,0 @@
-const { spawn } = require("child_process");
-const { appendFileSync } = require("fs");
-const { EOL } = require("os");
-
-function run(cmd) {
-  const proc = spawn(cmd, { stdio: "inherit", shell: true });
-  proc.on("exit", code => process.exitCode = code);
-}
-
-const key = process.env.INPUT_KEY.toUpperCase();
-if (process.env[`STATE_${key}`] !== undefined) {
-  // ---------- POST ----------
-  run(process.env.INPUT_POST);
-} else {
-  // ---------- MAIN ----------
-  appendFileSync(process.env.GITHUB_STATE, `${key}=true${EOL}`);
-  run(process.env.INPUT_MAIN);
-}