feat: add backend permission map and requirePermission middleware

Create the RBAC permission module that maps roles to permissions and
provides a requirePermission middleware to replace requireAdmin. Update
the test server to use requirePermission for the admin health check.

tests/unit/api/permissions.test.ts

@@ -0,0 +1,76 @@
+/**
+ * Unit tests for the permission map and helper functions.
+ *
+ * Verifies that each role gets the correct set of permissions
+ * and that the hasPermission check works as expected.
+ */
+
+import type { Role } from "@stirling-image/shared";
+import { describe, expect, it } from "vitest";
+import { getPermissions, hasPermission } from "../../../apps/api/src/permissions.js";
+
+describe("permissions", () => {
+  describe("getPermissions", () => {
+    it("returns all 12 permissions for admin", () => {
+      const perms = getPermissions("admin");
+      expect(perms).toHaveLength(12);
+      expect(perms).toContain("tools:use");
+      expect(perms).toContain("files:own");
+      expect(perms).toContain("files:all");
+      expect(perms).toContain("apikeys:own");
+      expect(perms).toContain("apikeys:all");
+      expect(perms).toContain("pipelines:own");
+      expect(perms).toContain("pipelines:all");
+      expect(perms).toContain("settings:read");
+      expect(perms).toContain("settings:write");
+      expect(perms).toContain("users:manage");
+      expect(perms).toContain("teams:manage");
+      expect(perms).toContain("branding:manage");
+    });
+
+    it("returns only basic permissions for user role", () => {
+      const perms = getPermissions("user");
+      expect(perms).toEqual([
+        "tools:use",
+        "files:own",
+        "apikeys:own",
+        "pipelines:own",
+        "settings:read",
+      ]);
+    });
+
+    it("does NOT contain admin-only permissions for user role", () => {
+      const perms = getPermissions("user");
+      expect(perms).not.toContain("files:all");
+      expect(perms).not.toContain("apikeys:all");
+      expect(perms).not.toContain("pipelines:all");
+      expect(perms).not.toContain("settings:write");
+      expect(perms).not.toContain("users:manage");
+      expect(perms).not.toContain("teams:manage");
+      expect(perms).not.toContain("branding:manage");
+    });
+
+    it("returns empty array for unknown role", () => {
+      const perms = getPermissions("unknown" as Role);
+      expect(perms).toEqual([]);
+    });
+  });
+
+  describe("hasPermission", () => {
+    it("returns true for admin with users:manage", () => {
+      expect(hasPermission("admin", "users:manage")).toBe(true);
+    });
+
+    it("returns true for user with tools:use", () => {
+      expect(hasPermission("user", "tools:use")).toBe(true);
+    });
+
+    it("returns false for user with users:manage", () => {
+      expect(hasPermission("user", "users:manage")).toBe(false);
+    });
+
+    it("returns false for user with settings:write", () => {
+      expect(hasPermission("user", "settings:write")).toBe(false);
+    });
+  });
+});