feat: Add GitHub App authentication support

[shit-agents]

Summary

Add native GitHub App authentication support to complement the existing PAT and OAuth methods.

Motivation

GitHub Apps are the recommended authentication method for integrations. They provide:

• Higher rate limits (5,000 requests/hour per installation)
• Granular repository permissions
• Bot identity for commits/PRs (shows as app-name[bot])
• No need to tie auth to a specific user account

Proposed Changes

1. Config additions (config/github-client.php)

'github_app' => [
    'app_id' => env('GITHUB_APP_ID'),
    'private_key' => env('GITHUB_APP_PRIVATE_KEY'),
    'private_key_path' => env('GITHUB_APP_PRIVATE_KEY_PATH'),
    'installation_id' => env('GITHUB_APP_INSTALLATION_ID'), // default installation
],

2. Installation token resource

New InstallationsResource to:

• List app installations (GET /app/installations)
• Get installation token (POST /app/installations/{id}/access_tokens)
• Cache tokens for ~55 minutes (they expire in 1 hour)

3. Connector enhancement

Allow GithubConnector to accept a GitHubAppAuthentication strategy that:

• Auto-refreshes installation tokens before expiry
• Falls back gracefully if app auth fails

4. Git operations resource (stretch)

Add methods for creating commits/PRs as the app:

• createBlob(), createTree(), createCommit(), updateRef()
• createBranch(), createPullRequest()

These are needed because commits made via the API (not git push) show the app as author.

Example Usage

use JordanPartridge\GithubClient\Facades\Github;

// Configure via .env, then:
$github = Github::forInstallation(98848199);
$github->repos()->get('the-shit/chat');

// Or with explicit config:
$github = Github::withApp(
    appId: '2443785',
    privateKey: file_get_contents('path/to/key.pem'),
    installationId: 98848199
);

Labels

enhancement, good first issue, agent

[jordanpartridge]

@shit-agents, love the concept please feel free to submit a pr