site: showcase appliance and DIY installation paths

[VijitSingh97]

What & why

The site still describes Pithead OS as unreleased and directs new users only to Docker Compose. Introduce both supported routes while preserving the existing visual style: an appliance card with image/checksum downloads and a flash guide beside a terminal containing the documented DIY setup commands.

Present appliance setup, signed system updates, backup/recovery, diagnostics, and headless operation alongside the existing mining, privacy, dashboard, and fleet features. Clarify optional beta defaults, refresh hardware/upgrade guidance and version badges, and align the social card and structured data. The copy explains the current product rather than promoting a version number.

Source: Pithead v2.0.0 release notes and its installation guides. The local layout has been reviewed by the requester; this PR remains open for final merge review.

Validation

• Strict Hugo 0.162.1 build
• htmltest 0.17.0 internal links, anchors, and images
• Node 22 / npm 10 install, Prettier, and Markdown lint
• codespell 2.4.2 and git diff --check
• Rendered download/checksum URLs match published release assets; JSON-LD parses and covers both routes
• Browser preview at desktop and 390px width; no horizontal overflow or browser errors
• README updated; landing copy remains in data/content.yaml

Based on main after Dependabot PR #41. Nine pre-existing development-tool audit findings remain; this content change adds no dependency or runtime request.