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.

.socket.json

@@ -0,0 +1,8 @@
+{
+  "issueRules": {
+    "critical": "error",
+    "high": "warn",
+    "medium": "ignore",
+    "low": "ignore"
+  }
+}