docs: fix Mintlify-incompatible links in security docs

Fix relative .md links to root-relative paths without extensions
as required by Mintlify docs system.

Changes:
- ./THREAT-MODEL-ATLAS.md -> /security/threat-model-atlas
- ./CONTRIBUTING-THREAT-MODEL.md -> /security/contributing-threat-model

Files updated:
- docs/security/README.md
- docs/security/THREAT-MODEL-ATLAS.md
- docs/security/CONTRIBUTING-THREAT-MODEL.md

docs/security/CONTRIBUTING-THREAT-MODEL.md

@@ -77,7 +77,7 @@ If you're unsure about the risk level, just describe the impact and we'll assess
 - [ATLAS Website](https://atlas.mitre.org/)
 - [ATLAS Techniques](https://atlas.mitre.org/techniques/)
 - [ATLAS Case Studies](https://atlas.mitre.org/studies/)
-- [OpenClaw Threat Model](./THREAT-MODEL-ATLAS.md)
+- [OpenClaw Threat Model](/security/threat-model-atlas)
 
 ## Contact
 

docs/security/README.md

@@ -4,8 +4,8 @@
 
 ## Documents
 
-- [Threat Model](./THREAT-MODEL-ATLAS.md) - MITRE ATLAS-based threat model for the OpenClaw ecosystem
-- [Contributing to the Threat Model](./CONTRIBUTING-THREAT-MODEL.md) - How to add threats, mitigations, and attack chains
+- [Threat Model](/security/threat-model-atlas) - MITRE ATLAS-based threat model for the OpenClaw ecosystem
+- [Contributing to the Threat Model](/security/contributing-threat-model) - How to add threats, mitigations, and attack chains
 
 ## Reporting Vulnerabilities
 

docs/security/THREAT-MODEL-ATLAS.md

@@ -21,7 +21,7 @@ This threat model is built on [MITRE ATLAS](https://atlas.mitre.org/), the indus
 
 ### Contributing to This Threat Model
 
-This is a living document maintained by the OpenClaw community. See [CONTRIBUTING-THREAT-MODEL.md](./CONTRIBUTING-THREAT-MODEL.md) for guidelines on contributing:
+This is a living document maintained by the OpenClaw community. See [CONTRIBUTING-THREAT-MODEL.md](/security/contributing-threat-model) for guidelines on contributing:
 
 - Reporting new threats
 - Updating existing threats