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>

docs/capabilities/INDEX.md

@@ -23,6 +23,7 @@ Indice de grupos de capacidades del registry. Cada grupo agrupa >=3 funciones qu
 | [notebook](notebook.md) | 5 | Operar Jupyter Lab colaborativo (discover/read/exec/write/kernel) |
 | [cpp-windows](cpp-windows.md) | 7 | Compilar, desplegar, lanzar y verificar apps C++ en Windows desde WSL2 |
 | [git](git.md) | 19 | Operaciones git y Gitea: clonar, commit, push/pull, hooks, TBD, webhooks, sync entre PCs |
+| [playwright](playwright.md) | 6 | E2E browser: launch chromium, login kanban, drag dnd-kit, keyboard sequence, wait predicate, assert class |
 
 ## Como anadir grupo