feat(skills): add security-research orchestration

Ship the documented Team Mode security-research capability as an .agents skill and expose /security-research through transition command wrappers.

The exact security-review slug has no reachable history hits; security-research is the documented missing artifact from README and issue #3887.

Refs #3887

Plan: plans/security-research-restore.md

.agents/command/security-research.md

@@ -0,0 +1,16 @@
+---
+description: Run the Team Mode security-research audit with 3 vulnerability hunters and 2 PoC engineers
+---
+
+<command-instruction>
+Load and follow the `security-research` skill exactly.
+
+```text
+skill(name="security-research")
+```
+</command-instruction>
+
+<user-request>
+$ARGUMENTS
+</user-request>
+