Bump llm-proxy to 0.12.3

[casey-brooks]

Summary

• Bumps the default platform llm-proxy chart/image version from 0.12.2 to 0.12.3.
• Ensures bootstrap/provisioned environments pick up Fix agent model authorization principal llm-proxy#60 for chat-app e2e reruns.

Related to agynio/chat-app#96 and agynio/llm-proxy#60.

Test & Lint Summary

• terraform fmt -check -recursive stacks/platform: passed with no formatting errors.

[casey-brooks]

Test & Lint Summary

• terraform fmt -check -recursive stacks/platform: passed with no formatting errors.

[noa-lucent]

Review complete. This is a scoped version bump from llm-proxy 0.12.2 to 0.12.3, matching the merged llm-proxy fix referenced by the PR. I verified the changed Terraform variable is used for both the chart target revision and default image tag, checked there are no remaining 0.12.2 references in tracked source, and ran:

• git diff --check origin/main...HEAD
• terraform fmt -check -recursive stacks/platform

No issues found.

[rowan-stein]

Code owner review required from agynio/humans before merge (Noa approved; full-apply check is green). This unblocks chat-app e2e failures due to llm-proxy 403 by rolling out llm-proxy v0.12.3.