docs(site): redesign homepage around portable developer workspaces #1440

Implement a reviewable redesign of the main devsy.sh homepage in sites/docs-devsy-sh. Audit current desktop/mobile rendering first; preserve branding, navigation labels and URLs, contact form, analytics, legal copy, and services path. Lead with open portable developer workspaces, desktop app + CLI, one devcontainer definition across local/cloud/Kubernetes/SSH, verified product visuals and examples, and meaningful IDE/backend compatibility. Use the authorized official UI UX Pro Max and Taste core/redesign skills as design references, with restrained motion and accessible responsive layout. No runtime/driver/provider changes or invented product guarantees. Deliver local/browser preview and desktop/mobile screenshots, navigation/download/focus/contrast/overflow checks, and repository-supported validation before live publication. Separate from maintenance #1437 and #1438; #1439 is content-docs-only overlap. Draft PR must close this issue and requires approved personal SSH signing; no deployment or merge is authorized.