feat(registry): add playwright capability group (6 TS browser fns)

New domain `browser` under frontend/functions/ with 6 Playwright helpers:
- pw_launch_browser: chromium + context + page bootstrap with storageState
  support and baseUrl navigation.
- pw_kanban_login: authenticates a Page against /api/auth/login; sets the
  kanban_session cookie via shared storageState; verifies login page no
  longer visible after navigation.
- pw_drag_drop: human-like pointer drag (mousedown + activateOffset +
  stepped move + mouseup) compatible with @dnd-kit/core's 8px activation
  threshold; supports hoverMs for time-based dropzones.
- pw_keyboard_sequence: ordered focus/type/press/wait steps for scripting
  realistic input flows (typing then arrow-key navigating autocompletes).
- pw_wait_predicate: thin wrapper over page.waitForFunction with friendlier
  defaults and custom error messages.
- pw_assert_class: poll-based assertion that a Locator has/lacks a CSS
  class within a timeout; useful for visual-state checks.

Each function ships with vitest tests (5-8 cases each) covering both happy
and error paths, plus self-documenting .md (Ejemplo + Cuando usarla +
Gotchas + frontmatter with params/output schema).

Adds frontend/functions/package.json with `"type": "module"` so consumers
can ESM-import the .ts files from anywhere in the registry (Playwright's
tsx loader respects nearest package.json).

Capability page docs/capabilities/playwright.md documents the group with
a canonical end-to-end example, frontiers, prerequisites, and gotchas.
Index updated.

First consumer (issue 0088): apps/kanban requester-input.spec.ts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/functions/browser/pw_kanban_login.test.ts

@@ -0,0 +1,104 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { pw_kanban_login } from "./pw_kanban_login";
+
+// --- mock helpers ---
+
+function makeResponse(status: number) {
+  return { status: () => status };
+}
+
+function makePage(overrides: {
+  currentUrl?: string;
+  postStatus?: number;
+  loginTextVisible?: boolean;
+} = {}) {
+  const currentUrl = overrides.currentUrl ?? "http://localhost:5180/login";
+  const postStatus = overrides.postStatus ?? 200;
+  const loginTextVisible = overrides.loginTextVisible ?? false;
+
+  const locatorMock = {
+    isVisible: vi.fn().mockResolvedValue(loginTextVisible),
+  };
+
+  return {
+    url: vi.fn().mockReturnValue(currentUrl),
+    request: {
+      post: vi.fn().mockResolvedValue(makeResponse(postStatus)),
+    },
+    goto: vi.fn().mockResolvedValue(undefined),
+    waitForLoadState: vi.fn().mockResolvedValue(undefined),
+    waitForSelector: vi.fn().mockResolvedValue(undefined),
+    locator: vi.fn().mockReturnValue(locatorMock),
+    _locatorMock: locatorMock,
+  };
+}
+
+// --- tests ---
+
+describe("pw_kanban_login", () => {
+  it("happy path", async () => {
+    const page = makePage({ postStatus: 200, loginTextVisible: false });
+
+    await pw_kanban_login(page as any, {
+      username: "egutierrez",
+      password: "secret",
+    });
+
+    // Should POST to derived origin + /api/login with correct body
+    expect(page.request.post).toHaveBeenCalledWith(
+      "http://localhost:5180/api/login",
+      { data: { username: "egutierrez", password: "secret" } },
+    );
+
+    // Should navigate to root
+    expect(page.goto).toHaveBeenCalledWith("http://localhost:5180/");
+
+    // Should wait for page load
+    expect(page.waitForLoadState).toHaveBeenCalledWith("networkidle");
+    expect(page.waitForSelector).toHaveBeenCalledWith("body", { state: "attached" });
+  });
+
+  it("rejects 401", async () => {
+    const page = makePage({ postStatus: 401 });
+
+    await expect(
+      pw_kanban_login(page as any, { username: "bad", password: "wrong" }),
+    ).rejects.toThrow("kanban login failed: 401");
+
+    // Should NOT navigate after failed login
+    expect(page.goto).not.toHaveBeenCalled();
+  });
+
+  it("rejects 500", async () => {
+    const page = makePage({ postStatus: 500 });
+
+    await expect(
+      pw_kanban_login(page as any, { username: "u", password: "p" }),
+    ).rejects.toThrow("kanban login failed: 500");
+  });
+
+  it("rejects when login page still visible", async () => {
+    // Simulate server returns 200 but login page is still showing (e.g. cookie not set)
+    const page = makePage({ postStatus: 200, loginTextVisible: true });
+
+    await expect(
+      pw_kanban_login(page as any, { username: "egutierrez", password: "secret" }),
+    ).rejects.toThrow("kanban login failed: login page still visible after authentication");
+  });
+
+  it("uses explicit baseUrl over page origin", async () => {
+    const page = makePage({ currentUrl: "http://localhost:5180/login", postStatus: 200 });
+
+    await pw_kanban_login(page as any, {
+      username: "egutierrez",
+      password: "secret",
+      baseUrl: "http://custom-host:9000",
+    });
+
+    expect(page.request.post).toHaveBeenCalledWith(
+      "http://custom-host:9000/api/login",
+      expect.any(Object),
+    );
+    expect(page.goto).toHaveBeenCalledWith("http://custom-host:9000/");
+  });
+});