docs(report): add section 5.3 draft assets

docs/temp-section-5-3-diagrams/5.3.2-authentication-and-sessions.md

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+# 5.3.2 User Authentication and Session Handling
+
+This diagram separates human user authentication from device-level authentication.
+
+```mermaid
+flowchart LR
+    User[User in Browser]
+    AuthAPI[/Better Auth Endpoints/]
+    Session[(session table)]
+    Users[(users table)]
+    Accounts[(account table)]
+    DeviceReg[/Device Registration API/]
+    DeviceToken[Signed Device Token]
+    DeviceAPI[/Device Auth Routes/]
+
+    User -->|sign up / sign in| AuthAPI
+    AuthAPI --> Users
+    AuthAPI --> Accounts
+    AuthAPI --> Session
+    Session -->|cookie-backed session| User
+
+    User -->|authenticated session| DeviceReg
+    DeviceReg -->|register browser as camera/client| DeviceToken
+    DeviceToken --> DeviceAPI
+
+    classDef auth fill:#e8f1ff,stroke:#2563eb,stroke-width:2px,color:#111827;
+    classDef data fill:#fff7e8,stroke:#d97706,stroke-width:2px,color:#111827;
+    class AuthAPI,DeviceReg,DeviceAPI,DeviceToken auth;
+    class Session,Users,Accounts data;
+```