feat: add official game-ci CLI with build, activate, and orchestrate commands

Introduces a yargs-based CLI entry point (src/cli.ts) distributed as the
`game-ci` command. The CLI reuses existing unity-builder modules — Input,
BuildParameters, Orchestrator, Docker, MacBuilder — so the same build
engine powers both the GitHub Action and the standalone CLI.

Commands: build, activate, orchestrate, cache (list/restore/clear),
status, version.

Closes #812

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/version.ts

@@ -0,0 +1,37 @@
+import type { CommandModule } from 'yargs';
+import * as core from '@actions/core';
+import fs from 'node:fs';
+import path from 'node:path';
+
+const versionCommand: CommandModule = {
+  command: 'version',
+  describe: 'Show version info',
+  builder: {},
+  handler: async () => {
+    try {
+      // Read version from package.json
+      let packageJsonPath = path.join(__dirname, '..', '..', '..', 'package.json');
+      if (!fs.existsSync(packageJsonPath)) {
+        packageJsonPath = path.join(__dirname, '..', '..', 'package.json');
+      }
+      if (!fs.existsSync(packageJsonPath)) {
+        packageJsonPath = path.join(process.cwd(), 'package.json');
+      }
+
+      if (fs.existsSync(packageJsonPath)) {
+        const packageData = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8'));
+        core.info(`game-ci (unity-builder) v${packageData.version}`);
+        core.info(`Node.js ${process.version}`);
+        core.info(`Platform: ${process.platform} ${process.arch}`);
+      } else {
+        core.info('game-ci (unity-builder)');
+        core.info('Version information unavailable');
+      }
+    } catch (error: any) {
+      core.info('game-ci (unity-builder)');
+      core.error(`Could not read version: ${error.message}`);
+    }
+  },
+};
+
+export default versionCommand;