[Docs] Add content depth to README

[roomote-roomote]

Opened on behalf of Matt Rubens. View the task or mention @roomote-roomote for follow-up asks.

What changed

Expanded the README with additional content depth for readers evaluating or contributing to Roomote:

• Table of Contents with anchor links for easier navigation
• Tech stack table showing the technology layers (Next.js, Hono, BullMQ, PostgreSQL, etc.)
• Communications and Integrations lines in the supported providers section
• Example tasks section with concrete prompt examples users can try
• Configuration reference table covering key environment variables
• Troubleshooting section for common issues (agent failures, sandbox clone errors, webhook delivery, database migrations, local reset)
• Contributing quick-start with essential commands

Why this change was made

The original README was strong on product positioning but light on practical reference material. Someone discovering Roomote for the first time had to click through to external docs for basic configuration, troubleshooting, and contribution workflows. This change brings the most-needed information into the README itself.

Impact

No user-facing behavior change. This is a documentation-only update that makes the project more approachable for new users and contributors.

[roomote-roomote]

2 issues outstanding. See task

• README.md:287-289 The new local-development sequence cannot start a fresh checkout: .env.local.example leaves R_PUBLIC_URL commented out, while pnpm dev rejects a missing public URL before starting services. Add a step to set a reachable HTTPS URL (and, if needed, ngrok credentials) before running pnpm dev.
• README.md:273 The configuration table marks R_APP_ENV as required and documents only development and production, but the environment schema makes it optional (defaulting to development) and also supports preview. Correct the requirement and accepted values so this reference does not reject a supported deployment mode.

_{Reviewed e8dab40}