docs: normalize frontmatter titles to sentence case

docs/security/CONTRIBUTING-THREAT-MODEL.md

@@ -1,5 +1,5 @@
 ---
-title: "Contributing to the Threat Model"
+title: "Contributing to the threat model"
 summary: "How to contribute to the OpenClaw threat model"
 read_when:
   - You want to contribute security findings or threat scenarios

docs/security/THREAT-MODEL-ATLAS.md

@@ -1,5 +1,5 @@
 ---
-title: "Threat Model (MITRE ATLAS)"
+title: "Threat model (MITRE ATLAS)"
 summary: "OpenClaw threat model mapped to the MITRE ATLAS framework"
 read_when:
   - Reviewing security posture or threat scenarios

docs/security/formal-verification.md

@@ -1,5 +1,5 @@
 ---
-title: Formal Verification (Security Models)
+title: Formal verification (security models)
 summary: Machine-checked security models for OpenClaw’s highest-risk paths.
 read_when:
   - Reviewing formal security model guarantees or limits