Polish the Parsar Core landing and onboarding documentation

[SaladDay]

New users were shown installation-time provider options before the supported zero-node flow, and Quickstart still required a local provider. README, the landing page and installation docs now lead with installing Core + Web + PostgreSQL, signing in, and adding a node through Web. Use Parsar Core naming, explain the reachable HTTPS origin before the first install, and keep unpublished distribution availability explicit.

Refine the desktop landing's existing light/purple style with clearer typography, a dark API example, a shared Runtime diagram and numbered installation steps. Correct related operations guidance for paired console authentication, transport routes, credential backups and node readiness.

Scope: static site HTML/CSS and documentation only. No application, installer, API, Runtime, dependencies or generated contracts changed. No new framework or website/release publication. Further mobile work is deferred at the user's request.

Validation:

• Real Chromium desktop rendering at 1440 and 1280px, links/anchors, resource errors, overflow and keyboard focus checked. Final title/layout adjustment passed at both desktop widths.
• Documentation links/anchors and the displayed install command checked against actual files and shell arguments.
• make check was run on the original docs candidate. It exited 2: 113/117 browser cases passed; four existing Web failures were reproduced once on source identical to main baseline 437858d. The complete Web/client trees, test configuration and lockfile are unchanged by this PR. These failures are recorded separately as WEB-TEST-002; no test assertions or application semantics were changed here.
• Prior gate stages passed, including real PostgreSQL, Go, installer, SDK, client and Web unit/build checks. Remaining MiniMax and Rust targets were run separately and passed. Subsequent changes are static landing presentation only and receive desktop rendering checks; no paid model rerun was needed.
• Integrated latest main 88e5700 after Show sandbox nodes around Core and simplify node enrollment #59 updated node enrollment. Resolved documentation conflicts in favor of its automatic console origin and Add node dialog; retained the revised install/login sequence. No upstream application changes are part of this PR diff. The integration received focused copy/layout verification, not another full application regression.
• Fresh GPT-6 Astra high independent review completed. Inline link distinction and small-label contrast were corrected; the bounded CSS fixes passed focused verification and self-review (default inline-link underlines and 5.74:1 label contrast).

Known baseline failures: a selector matches a hidden cached Dashboard label; live and durable tooltip expectations differ from current numeric projections; Session-page request counts differ after navigation. Their intended product semantics require separate assessment, especially missing-value projection. This PR does not claim a green repository-wide gate.

The repository is private. GitHub documentation paths resolve in the checkout but anonymous requests return 404; public visitor access and release publication remain separate delivery work.