docs: rewrite guides and simplify documentation pages

[jouwdan]

Rewrites all 92 documentation files as concise, neutral instructions and simplifies the documentation site using the brand's typography, colors, and layout conventions.

• Move deployment guides into Getting started while preserving existing URLs.
• Keep a complete Coolify walkthrough covering setup, domains, secrets, storage, deployment checks, backups, and maintenance.
• Check instructions against the implementation and correct stale behavior, defaults, and lifecycle descriptions.
• Use pnpm by default, with documented npm exceptions for generated boards and registry operations.
• Regenerate references from their sources and update wording-dependent consumers and tests.

Validation:

• pnpm verify — passed; 9,244 tests passed.
• pnpm site:build — passed.
• Website Playwright suite — all 6 tests passed using installed Chrome.
• Documentation links, index, generated references, and inline-comment checks — passed.
• Manual desktop/mobile and light/dark review, including the full Coolify guide.