Add canonical public index for VERIFRAX evidence surface

[midiakiasat]

Why

VERIFRAX evidence is now materially present, but without a single public root index it remains harder for auditors, claimants, challengers, and adversarial readers to navigate what exists, what was executed, and what boundary is actually proven.

Included surface

• evidence/README.md

Result

• establishes a canonical public navigation root for VERIFRAX evidence
• makes bootstrap status, artifact objects, execution outputs, gap surfaces, and package publication evidence discoverable from one place
• improves transparency for adversarial review without changing any underlying verdict object

Boundary

This change adds evidence navigation only. It does not alter authority artifacts, semantic outputs, or bootstrap-chain conclusions.