docs: update website with latest features

[nomadicmehul]

Summary

• Commands section: added dispatch schedule and dispatch stats (4 → 6 commands)
• Added --engine and --no-telemetry flags to dispatch run
• Updated "Extensible Engine" feature → "Multi-Engine Support" (Gemini & GitHub Models are shipped)
• Roadmap: moved Multi-Engine to "Shipped", added Scheduled Runs & Telemetry as "Shipped"
• Fixed OG URL to use dispatchai.dev custom domain

Test plan

• Verify website renders correctly at dispatchai.dev after merge
• Check new command cards display properly
• Verify roadmap timeline reflects current state