Wire operator Integrations page + capability-gating framework

Completes the arcadia-admin operator surface for the integration registry and
the capability/route-guard framework it depends on.

- Integration registry: route + Data-group nav entry + `platform.integrations`
  capability; the in-app client now delegates to the shared
  `@crema/integration-registry-client` lib (vite alias + tsconfig); the
  operator Integrations page (committed earlier) is now reachable.
- Capability gating: capabilities map + route-guard + jwt helpers + the
  apps/plan/entitlements routes and supporting tenants/session changes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/lib/jwt.ts

@@ -0,0 +1,49 @@
+// Tiny JWT helpers — we never *verify* tokens client-side (the server
+// is the only authority), we just decode the payload to read claims
+// the UI uses for nav gating + tenant context.
+
+export type ArcadiaClaims = {
+  sub?: string
+  email?: string
+  tenant_id?: string
+  tenant_slug?: string
+  roles?: string[]
+  available_tenants?: AvailableTenantClaim[]
+  exp?: number
+  iat?: number
+  [k: string]: unknown
+}
+
+export type AvailableTenantClaim = {
+  id?: string
+  slug?: string
+  name?: string
+  roles?: string[]
+}
+
+function b64urlDecode(s: string): string {
+  const pad = "=".repeat((4 - (s.length % 4)) % 4)
+  const b64 = (s + pad).replace(/-/g, "+").replace(/_/g, "/")
+  if (typeof atob === "function") return atob(b64)
+  // Node fallback (SSR / tests)
+  return Buffer.from(b64, "base64").toString("binary")
+}
+
+export function decodeJwt(token: string): ArcadiaClaims | null {
+  if (!token) return null
+  const parts = token.split(".")
+  if (parts.length !== 3) return null
+  try {
+    const raw = b64urlDecode(parts[1])
+    // Handle UTF-8: atob returns binary string; reconstruct UTF-8.
+    const utf8 =
+      typeof TextDecoder !== "undefined"
+        ? new TextDecoder().decode(
+            Uint8Array.from(raw, (c) => c.charCodeAt(0)),
+          )
+        : raw
+    return JSON.parse(utf8) as ArcadiaClaims
+  } catch {
+    return null
+  }
+}