docs: polish README entry paths without losing deep technical content - #171

Scope: deliberate micro-adjustment

Preserve the existing hero SVG, badges, Proof Lab CTA, Bluefin and Claude flagship cases, 30-second onboarding, advanced CLI documentation, and evidence limitations.

Changes

• Add a compact Find your path table to route first-time readers to demo, install, real evidence, external interop, or advanced semantics.
• Clarify immediately that browser fixtures are illustrative and CLI/Action are actual evidence-producing paths.
• Add a collapsible explanation of proof scope and non-claims.
• Surface the external evidence ledger next to the Reality Lab instead of claiming unsupported adoption.

Checks requested

• GitHub Markdown rendering (especially table and <details>), narrow-screen hero readability, and relative/anchor links.
• Documentation-only; no product logic changed.

No existing sections removed. Ready for review before merge.