feat: integrate OIDC token exchange in GitHub Action

- Add setupGitHubInstallationToken utility for OIDC token generation
- Implement automatic token exchange with Pullfrog API endpoint
- Add support for multiple authentication methods (input, env, OIDC)
- Create setup utilities for test repository management
- Update action entry point to handle new token flow
- Add environment variable documentation for API key
- Remove large bundled dependencies and optimize build
- Support both development and production token workflows

utils/github.ts

@@ -0,0 +1,56 @@
+import * as core from "@actions/core";
+
+/**
+ * Setup GitHub installation token for the action
+ */
+export async function setupGitHubInstallationToken(): Promise<string> {
+  // Check if we have an installation token from inputs or environment
+  const inputToken = core.getInput("github_installation_token");
+  const envToken = process.env.GITHUB_INSTALLATION_TOKEN;
+  
+  const existingToken = inputToken || envToken;
+  if (existingToken) {
+    core.info("Using provided GitHub installation token");
+    return existingToken;
+  }
+
+  core.info("No cached installation token found, generating OIDC token...");
+
+  try {
+    // Generate OIDC token for our API
+    const oidcToken = await core.getIDToken("pullfrog-api");
+    core.info("OIDC token generated successfully");
+
+    // Exchange OIDC token for installation token
+    const apiUrl = process.env.API_URL || "https://pullfrog.ai";
+
+    const tokenResponse = await fetch(`${apiUrl}/api/github/installation-token`, {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${oidcToken}`,
+        "Content-Type": "application/json",
+      },
+    });
+
+    if (!tokenResponse.ok) {
+      const errorText = await tokenResponse.text();
+      throw new Error(
+        `Token exchange failed: ${tokenResponse.status} ${tokenResponse.statusText} - ${errorText}`
+      );
+    }
+
+    const tokenData = await tokenResponse.json();
+    core.info(
+      `Installation token obtained for ${tokenData.owner}/${tokenData.repository || "all repositories"}`
+    );
+
+    // Set the token as an environment variable for this run
+    process.env.GITHUB_INSTALLATION_TOKEN = tokenData.token;
+
+    return tokenData.token;
+  } catch (error) {
+    throw new Error(
+      `Failed to setup GitHub installation token: ${error instanceof Error ? error.message : "Unknown error"}`
+    );
+  }
+}