fix(security): Set Secure flag on session cookies

[justin-layerv]

Summary

Set the Cookie Secure attribute to true for session cookies in KBS auth and attest handlers.

Problem

Session cookies were being set with Secure: false, allowing them to be transmitted over unencrypted HTTP connections. This could expose session IDs to interception via man-in-the-middle attacks.

Changes

File	Change
endpoints/server/kbs/auth/auth.go	Set Cookie Secure flag to true
endpoints/server/kbs/attest/attest.go	Set Cookie Secure flag to true

Test plan

• Verify build passes
• Verify cookies are correctly set with Secure flag in HTTPS environments
• Confirm KBS authentication flow still works correctly

🤖 Generated with Claude Code

[craftleon]

Merging is blocked due to commit missing verified signatures.