docs: log silhouette-first edge snap + inset removal findings

Record v1.087 detection conclusions in the engineering log so the next
session does not retry the strongest-gradient rule or re-add the inset.

Constraint: log entries state measured results only, no speculation.
Confidence: high
Scope-risk: local
Reversibility: trivial
Directive: none
Tested: markdown-only change, table renders correctly.
Not-tested: n/a
Related: f5d2fa7

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