Fix jev_verify handling of evidence IDs named none

[xujiantop-crypto]

Summary

jev_verify uses none as an internal no-source option when multiple evidence items are supplied. If a caller provides a real evidence item whose ID is also none, the internal option overwrites that evidence entry in the choice criteria. A model response selecting the real evidence is then incorrectly returned as supporting_evidence: null.

This change:

• allocates a collision-free internal key for the no-source option
• preserves caller-provided evidence IDs, including none
• validates source answers against the generated internal key
• adds an end-to-end mock regression test for the collision

Reproduction

Call jev_verify with multiple evidence items, including { id: "none", ... }, and have Jev select that evidence as the claim source. Before this fix, the request criteria replace the real none entry with the no-source description and the result loses the selected evidence ID.

Verification

• npm test — 225/225 passing
• npm run typecheck
• npm run build
• git diff --check

[jkudish]

• Thanks for this — a real bug: jev_verify's internal no-source option collided with evidence literally named "none".
• The fix looks good as sent: collision-free internal key, same pattern jev_classify uses.
• Merged with one small test addition (also covering the none_1 suffix case).
• Shipping in the next patch release.