feat: implement sensitive data redaction for viewer roles

- Introduced SensitiveConnectionValue component to handle redaction of sensitive connection details across the frontend.
- Updated API to include canViewServerConnection and canViewEnvironmentValues functions to determine access based on user roles.
- Enhanced backend response sanitization to remove sensitive data for viewer roles, ensuring no sensitive information is exposed in API responses.
- Applied redaction logic in various components including ServersTable, DomainsTable, and EnvironmentHeader to maintain UI consistency while hiding sensitive information.
- Added comprehensive audit documentation outlining the implementation and maintenance rules for sensitive data handling.

src/components/SensitiveConnectionValue.tsx

@@ -0,0 +1,35 @@
+interface SensitiveConnectionValueProps {
+  value?: string | null;
+  isRedacted: boolean;
+}
+
+/** Keeps connection fields discoverable without exposing their values to viewers. */
+export default function SensitiveConnectionValue({
+  value,
+  isRedacted,
+}: SensitiveConnectionValueProps) {
+  if (!isRedacted) {
+    return <>{value || "—"}</>;
+  }
+
+  return (
+    <span
+      aria-label="Connection address hidden for viewer"
+      title="Connection address hidden"
+      style={{
+        display: "inline-flex",
+        alignItems: "center",
+        borderRadius: 4,
+        padding: "2px 7px",
+        background: "var(--bg-input)",
+        border: "1px solid var(--border)",
+        color: "var(--text-muted)",
+        fontSize: 10,
+        letterSpacing: "0.08em",
+        userSelect: "none",
+      }}
+    >
+      ••••••••••••
+    </span>
+  );
+}