feat: add social-graph-ranker skill — weighted network proximity scoring

New skill: social-graph-ranker
- Weighted social graph traversal with exponential decay across hops
- Bridge Score: B(m) = Σ w(t) · λ^(d(m,t)-1) ranks mutuals by target proximity
- Extended Score incorporates 2nd-order network (mutual-of-mutual connections)
- Final ranking includes engagement bonus for responsive connections
- Runs in parallel with lead-intelligence skill for combined warm+cold outreach
- Supports X API + LinkedIn CSV for graph harvesting
- Outputs tiered action list: warm intros, direct outreach, network gap analysis

Added to business-content install module. Catalog validates: 30/60/140.

manifests/install-modules.json

@@ -273,7 +273,9 @@
         "skills/content-engine",
         "skills/investor-materials",
         "skills/investor-outreach",
-        "skills/market-research"
+        "skills/lead-intelligence",
+        "skills/market-research",
+        "skills/social-graph-ranker"
       ],
       "targets": [
         "claude",