[Electric 2.0] Rewrite Quickstart Guide

## Goal
<5 min local setup, <10 min production deploy with claimable resources

## Scope
- Focus purely on getting starter running
- Claimable resources flow clearly explained
- Remove/minimize Docker Compose complexity

## Current File
`/website/docs/quickstart.md` (239 lines)

## Dependencies
Claimable resources feature must be live in Cloud (see stratovolt#713)

## Acceptance Criteria
Developer feedback that setup is < 5 min

## Context
Part of Electric 2.0 launch. The quickstart is the first impression - it needs to be fast and delightful.