[Subsystem] Implement Authentication, Session Context & View Security Guards (Port of Ivy/Auth)

Problem Statement

Ivy-Framework (C#) in src/Ivy/Auth provides JWT/Cookie session management, authentication middleware, identity provider context, and view security guards.

Rusty-Framework currently has no built-in authentication layer, auth context hooks, or view security guard primitives.

Missing Functionality

• JWT and cookie session management middleware in rusty-server.
• Authentication context hooks (use_auth, use_user) for accessing active session identity state in Rust views.
• Security guard component wrapper / attribute (Guard) to restrict rendering based on roles, claims, or permissions.
• Security headers and silent token renewal helpers.

Proposed Architecture & Design

1. Implement auth middleware for rusty-server using Axum/Tower layer abstractions.
2. Create AuthContext and hooks use_auth() and use_user() in rusty::hooks.
3. Implement Guard wrapper widget in rusty::widgets that evaluates AuthContext before rendering children.
4. Support standard authentication workflows (Login, Logout, Token Refresh, Role verification).

Acceptance Criteria

• Auth middleware validates JWT tokens and session cookies in rusty-server.
• use_auth hook provides reactive user identity and session status.
• Guard widget selectively renders child components based on user roles and permissions.
• Integration tests verifying authenticated vs unauthenticated rendering states.

Start by reading the reference implementation in src/Ivy/Auth, then inspect the rusty-server, rusty::hooks, and rusty::widgets entry points named in the proposal. Define the auth middleware, AuthContext hooks, Guard behavior, and integration-test scope from the acceptance criteria; done requires JWT and cookie validation, reactive identity state, role or permission-based rendering, and authenticated versus unauthenticated tests.