Document the supported-browser matrix (browsers, ClickHouse versions, IdP requirements)

Part of #68 (Roadmap to 1.0.0) — release-blocker.

Problem

The README never states which browsers/versions are supported, nor the supported ClickHouse versions or IdP requirements. A 1.0 cannot ship silent on this — especially given the html{zoom} reliance (see the zoom de-risk + WebKit-e2e issues), which makes the supported-engine set a real, non-obvious constraint.

Ask

Add a concise support matrix / system-requirements section to the README:

• Browsers + minimum versions (desktop Chrome/Edge/Firefox; Safari status pending the WebKit decision). Note desktop-only if that's the call (no responsive CSS today).
• ClickHouse server versions (incl. Antalya vs OSS + JWT-verify sidecar notes).
• IdP/OAuth requirements (PKCE public client preferred; the client_secret caveat → link SECURITY.md).

Acceptance

• README has a clear, scannable support matrix.
• Browser row reflects the WebKit/Safari decision from the related issues.

Folded in from the roadmap (#68) nice-to-haves:

• State the desktop-only stance explicitly — there is no responsive CSS today (no @media, fixed px, overflow:hidden on html/body). The matrix should say "desktop browsers" (or add a minimal narrow-viewport fallback) so a phone/tablet user isn't surprised by a silently-broken layout.

ClickHouse 24.8 decision (#627)

ClickHouse 24.8 is Limited support: query execution and Table results are
supported. Typed result features such as automatic charts, KPI interpretation,
logs detection, and type-aware formatting may be unavailable because 24.8 does
not provide result metadata in the streaming format used by SQL Browser.

SQL Browser does not infer ClickHouse result types from returned values.
Do not describe 24.8 as full-fidelity support. #627 is the production
compatibility implementation and live-verification record.

Start with README and review SECURITY.md, the related WebKit/Safari and zoom issues, and #627 for the ClickHouse 24.8 compatibility decision. Document the browser matrix, desktop-only stance, ClickHouse support and limitations, and IdP requirements, with the Safari row matching the WebKit decision.