feat(tooling): add .socket.json and Filter 9 to evaluate-library skill

Add repo-root .socket.json (critical=error, high=warn, medium/low=ignore)
and extend the evaluate-library skill's 8-filter protocol to 9 filters by
adding Filter 9 — Supply-chain behavior (Socket). Positions Socket last in
Phase 2 (most expensive: network call), documents socket-cli as the
verification command, and maps clean/flagged/<finding-summary> to the
trace's socketRisk field. Updates short-circuit skip lists for all earlier
Phase 2 filters and adds socketRisk to TRACE-TEMPLATE.md frontmatter.

.claude/skills/evaluate-library/TRACE-TEMPLATE.md

@@ -26,6 +26,7 @@ filter-results:
   eu-residency: ok | n/a | self-hostable | fail
   cve-scan: clean | "<advisory-id>" | fail
   named-consumer: pass | fail
+  socketRisk: clean | flagged | <finding-summary>
 verification-commands:
   - <literal command that produced the license result>
   - <literal command that confirmed types>
@@ -59,6 +60,7 @@ filter-results:
   eu-residency: skip
   cve-scan: skip
   named-consumer: skip
+  socketRisk: skip
 verification-commands:
   - npm view <pkg> time.modified
 accepted-cves: []