feat: add UserRole RBAC framework for multi-user support

- UserRole enum: Admin (full), Viewer (read-only), AppUser (minimal)
- can_access() method checks RPC method against role permissions
- Role field on User struct with serde default (backward-compatible)
- Viewer: read system/federation/DWN/identity/backup/container status
- AppUser: system.stats, node.did, container list, password change

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/auth.rs

@@ -8,6 +8,60 @@ use tokio::fs;
 
 use crate::totp::TotpData;
 
+/// User role for multi-user RBAC (Year 3 feature).
+/// - Admin: full access to all operations
+/// - Viewer: read-only dashboard, container status, monitoring
+/// - AppUser: access specific apps, no system configuration
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "lowercase")]
+pub enum UserRole {
+    Admin,
+    Viewer,
+    AppUser,
+}
+
+impl Default for UserRole {
+    fn default() -> Self {
+        UserRole::Admin
+    }
+}
+
+impl UserRole {
+    /// Check if this role allows a given RPC method.
+    pub fn can_access(&self, method: &str) -> bool {
+        match self {
+            UserRole::Admin => true,
+            UserRole::Viewer => {
+                // Read-only methods
+                method.starts_with("system.")
+                    || method.starts_with("node.")
+                    || method.starts_with("federation.list")
+                    || method.starts_with("dwn.status")
+                    || method.starts_with("dwn.list")
+                    || method.starts_with("dwn.query")
+                    || method.starts_with("identity.list")
+                    || method.starts_with("identity.get")
+                    || method.starts_with("backup.list")
+                    || method == "container-list"
+                    || method == "container-status"
+                    || method == "container-health"
+                    || method == "health"
+                    || method == "auth.logout"
+            }
+            UserRole::AppUser => {
+                // App access + basic read
+                method.starts_with("system.stats")
+                    || method == "node.did"
+                    || method == "container-list"
+                    || method == "container-status"
+                    || method == "health"
+                    || method == "auth.logout"
+                    || method == "auth.changePassword"
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 struct OnboardingState {
     complete: bool,
@@ -21,6 +75,9 @@ pub struct User {
     pub onboarding_complete: bool,
     #[serde(default)]
     pub totp: Option<TotpData>,
+    /// User role for RBAC (defaults to Admin for backward compatibility)
+    #[serde(default)]
+    pub role: UserRole,
 }
 
 #[allow(dead_code)]