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_wait_predicate.ts

@@ -0,0 +1,45 @@
+import type { Page } from "playwright";
+
+/** Options for pw_wait_predicate. */
+export interface PwWaitOptions {
+  /** Maximum time to wait in milliseconds. Default: 5000 */
+  timeoutMs?: number;
+  /** Polling interval in milliseconds. Default: 100 */
+  pollMs?: number;
+  /** Argument passed to the predicate function in the page context. */
+  arg?: unknown;
+  /** Custom error message prepended to the timeout error. */
+  message?: string;
+}
+
+/**
+ * pw_wait_predicate — polls an arbitrary predicate inside the page context
+ * until it returns truthy or the timeout elapses.
+ *
+ * Thin wrapper around `page.waitForFunction` with friendlier defaults and
+ * optional custom error messages. More flexible than `waitForSelector` for
+ * computed conditions such as "card has class .border-red" or "exactly 1
+ * element is highlighted".
+ */
+export async function pw_wait_predicate<T = unknown>(
+  page: Page,
+  predicate: string | ((arg?: unknown) => unknown),
+  opts: PwWaitOptions = {},
+): Promise<T> {
+  const timeoutMs = opts.timeoutMs ?? 5000;
+  const pollMs = opts.pollMs ?? 100;
+
+  try {
+    const handle = await page.waitForFunction(predicate, opts.arg, {
+      timeout: timeoutMs,
+      polling: pollMs,
+    });
+    return handle.jsonValue() as Promise<T>;
+  } catch (err) {
+    if (opts.message) {
+      const cause = err instanceof Error ? err : new Error(String(err));
+      throw new Error(`${opts.message}: ${cause.message}`, { cause });
+    }
+    throw err;
+  }
+}