chore: add scout.personas.yaml for Scout agent

[samtuckerdavis]

Summary

• Adds scout.personas.yaml defining four caller personas for the Scout agent to exercise the proxy's API surface and privacy guarantees.

Personas

ID	Purpose
investigation-tool	Tier 3 sensitive-content caller — verifies zero-retention invariant and security headers (HSTS, X-Content-Type-Options, X-Frame-Options)
advocacy-tool	Standard campaign automation caller — exercises chat completions, embeddings, and model listing via OpenAI-compatible client
privacy-auditor	Sends canary strings to confirm prompt content is never echoed in response headers, error bodies, or metadata
health-probe	Unauthenticated /health probe — confirms 200 without auth and no internal state leakage

Key assertions covered

• Valid bearer token → 200 with choices array
• Missing/invalid key → 401 (not 500), generic error message only
• Rate-limit breach → 429 (not 500)
• PRIVATEMODE_API_KEY never appears in any response
• Request prompt content (choices field) absent from all logs and response headers
• HSTS, X-Content-Type-Options, X-Frame-Options present on all authenticated responses
• /health returns {"status": "healthy"} with no auth required and no internal state disclosed

No production code changed

This PR adds only a YAML configuration file; no application logic is touched.

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📥 Commits

Reviewing files that changed from the base of the PR and between 8c032a6 and f329039.

📒 Files selected for processing (1)

• scout.personas.yaml

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/add-scout-personas

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