Add E2E and behavioural tests for validate-audit.js workflow and Makefile audit targets

[coderabbitai]

Summary

Makefile audit tests exercise only dry-run command strings; no end-to-end or behavioural tests exist for the validate-audit.js workflow or for actual Makefile target execution.

Problems

• scripts/makefile-audit.test.mjs verifies only that expected command strings appear in make --dry-run output; it does not execute the targets with real tools.
• validate-audit.js has no tests that exercise the assertValidSchema and assertMitigated orchestration paths with real or mock advisories.
• There are no behavioural tests that verify audit execution failure paths (e.g. unexpected advisory detected, schema validation error).

Acceptance criteria

• Add integration or behavioural tests for the validate-audit.js orchestration, covering:
  • assertValidSchema with valid and invalid exception-ledger JSON.
  • assertMitigated with a match between advisories and the exception ledger (no error), and with an unmatched advisory (error + non-zero exit).
• Add behavioural tests that execute relevant Makefile targets (audit-node, rust-audit) with actual (or suitably shimmed) tool behaviour rather than dry-run string checks.

Context

Raised during review of PR #354 by @leynos.

[coderabbitai]

🔗 Related PRs

#350 - Extract audit fallback test setup [merged]
leynos/corbusier#79 - Add joint Rust and node audit gate [merged]
leynos/theoremc#44 - Run Rust tests with cargo-nextest [merged]
leynos/netsuke#309 - Expand top-level action flow control (3.14.2) [merged]
leynos/vibe-coder#7 - Record XState machine collocation strategy (1.1.3) [closed]

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