[Electric 2.0] Update Homepage for 2.0 Launch

## Goal
Reflect Electric 2.0 positioning on main site

## Scope
- Hero messaging: "Query-driven sync with your stack"
- Feature callouts: subqueries, TanStack DB
- Update `/website/index.md` and home components

## Dependencies
All features shipped, messaging finalized

## Acceptance Criteria
Homepage tells complete 2.0 story

## Context
Part of Electric 2.0 launch. The homepage is the first thing visitors see - it needs to communicate the complete 2.0 vision.