Add GitHub worker for processing webhooks and fetching markdown files

[devin-ai-integration]

Add GitHub worker for processing webhooks and fetching markdown files

Summary

This PR introduces a new github-worker package that processes GitHub webhooks to automatically fetch and store .md and .mdx files from repositories. The worker implements:

• Webhook Processing: Handles GitHub push and pull_request events with HMAC-SHA256 signature verification
• GitHub API Integration: Recursively fetches all markdown files from repositories with retry logic and rate limiting handling
• Versioned Database Storage: Uses Cloudflare Durable Objects to store files with version tracking via SQL database
• Modular Architecture: Clean separation between webhook handling, GitHub API client, and database operations

The implementation follows existing monorepo patterns and integrates with the Cloudflare Workers ecosystem using wrangler configuration.

Review & Testing Checklist for Human

⚠️ CRITICAL - This PR requires extensive testing as the core functionality could not be fully verified locally

• End-to-end webhook testing: Set up a test repository with GitHub webhooks pointing to the deployed worker and verify files are correctly fetched and stored
• Security verification: Test webhook signature verification with real GitHub webhook payloads to ensure HMAC-SHA256 implementation is correct
• Database operations: Verify the SQL schema creation, versioned upsert functionality, and data retrieval work correctly in the Durable Object environment
• GitHub API integration: Test with repositories containing various .md/.mdx file structures, including nested directories and edge cases
• Error handling: Verify graceful handling of GitHub API rate limits, authentication failures, and malformed webhook payloads

Recommended test plan: Deploy to a staging environment, configure webhooks on a test repository with various markdown files, trigger events, and verify data storage and retrieval.

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TB
    GitHub["GitHub Repository<br/>(webhook source)"] --> Webhook["github-worker/src/webhook.ts<br/>Webhook Handler"]:::major-edit
    Webhook --> API["github-worker/src/github-api.ts<br/>GitHub API Client"]:::major-edit
    API --> Database["github-worker/src/database.ts<br/>Durable Object DB"]:::major-edit
    
    Index["github-worker/src/index.ts<br/>Main Worker"]:::major-edit --> Webhook
    Types["github-worker/src/types.ts<br/>Type Definitions"]:::major-edit --> Database
    Types --> API
    Types --> Webhook
    
    Config["github-worker/wrangler.toml<br/>Worker Configuration"]:::major-edit --> Index
    PackageRoot["package.json<br/>(root workspace)"]:::minor-edit --> PackageWorker["github-worker/package.json"]:::major-edit
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• TypeScript types: Had to use any types in several places due to Cloudflare Workers type system complexity - this should be revisited for better type safety
• Local testing limitations: Could not fully test the worker locally due to missing wrangler installation and Cloudflare runtime dependencies
• Security consideration: The webhook signature verification is critical for security - ensure the GITHUB_WEBHOOK_SECRET environment variable matches your GitHub webhook configuration
• Database schema: The versioned upsert approach maintains file history - consider storage implications for repositories with frequent changes

Link to Devin run: https://app.devin.ai/sessions/154eef22d18b4ecd9a571780c03094d8
Requested by: @nathanclevenger

[devin-ai-integration]

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