ci: drop audit.yml and audit config

[lwshang]

Description

This PR removes the cargo audit CI workflow (.github/workflows/audit.yml) and its associated config (.cargo/audit.toml).

Motivation:

• This repo is being deprecated. The audit CI runs on a daily cronjob, and its failures are more noise than signal for us at this point.
• Dependabot already provides similar coverage of vulnerable dependencies, so dropping the audit job doesn't leave us blind.
• The audit check has already been removed from the required checks in the branch protection rule, so removing the workflow won't block merges.

How Has This Been Tested?

N/A — this only removes a CI workflow and its config.

Checklist:

• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to 7012e78.

Security Overview

• 🔎 Scanned files: 2 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/54bfa532-d98c-41d3-a572-866d55d9f461?scanId=376fdfa8-af6a-4949-8162-de36b67a3793&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Configuration changes	► .cargo/audit.toml     Remove advisory ignore list ► .github/workflows/audit.yml     Remove audit workflow configuration