feat: add authentication middleware

[rodchalski]

New auth middleware for session validation. Expected: APPROVAL REQUIRED

[permission-protocol]

🔒 Permission Protocol

🚨 This PR requires human authorization before merge.

---

⚠️ Risk Detected

Changes to authentication or session handling in src/middleware/auth.ts could disrupt user sign-in

Property	Value
Risk Level	🔴 High — Auth
Impact	Changes to authentication or session handling in src/middleware/auth.ts could disrupt user sign-in
File	src/middleware/auth.ts
Status	⛔ Awaiting authorization

---

👉 🔓 Authorize this change →

_{A designated reviewer must authorize before this PR can merge.}

---

📋 Why was this flagged?

• Changes to authentication or session handling in src/middleware/auth.ts could disrupt user sign-in
• Changed files: src/middleware/auth.ts

✅ Verify before authorizing

• Confirm src/middleware/auth.ts behaves correctly after deploy

---

_{🔒 Permission Protocol · Decision: approval required by policy}