Popup support: wrap popup pages with addPlugins - #32

Wrapped pages listen for the popup event and wrap the popup
automatically (recursively for nested popups). Plugins may declare
forPopup(ctx) to produce the popup's plugin - videoMode returns null for
now (its parent-bound child recorder is phase 2) - and plugins without
the hook are re-registered as-is, which is safe for the stateless ones.
Opt out with popups: false; children dispose before the parent
finalizes.

addPlugins on an already-wrapped page now throws instead of silently
replacing plugin state mid-flight - this also guards accidental double
wrapping of main pages. Manual popup wrapping (the #32 pattern) becomes
the popups: false path; specs migrated accordingly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Replaces #33 (stack tooling wouldn't let its base move off the
now-closed #32). Complete popup support, from the approved design in
`tasks/complete/2026-08-13-popup-overlay-video.md` — includes what was
#32 (popup wrapping + per-instance videoMode artifact namespacing) plus:

1. **Auto-wrap**: pages wrapped with `addPlugins` automatically wrap
popups they open (recursively) — spinner-waiting, error reporting etc.
apply to the popup with zero test wiring. Plugins control their popup
behavior via a `forPopup(ctx)` hook; opt out wholesale with `popups:
false`. Wrapping an already-wrapped page now throws.
2. **Overlay video**: instead of a separate `-2` video, the popup
renders as an overlay **in the main page's video** — it slides up from
the bottom over the dimmed page, popup clicks and typed fill reveals are
annotated inside it (focus ring included), one cursor glides between
page and popup, and it slides away on close. Implemented as a two-pass
render: a composite pass over the raw screencasts, then the existing
annotation machinery unchanged. Popup facts land in `video-mode.json`
under `children` (schema v2).

```ts
// test code stays completely ordinary:
const popupPromise = page.waitForEvent("popup");
await page.getByRole("button", { name: "Sign in" }).click();
const popup = await popupPromise; // already wrapped — no addPlugins call
await popup.getByLabel("Username").fill("mmkal");
await popup.getByRole("button", { name: "Sign in" }).click();
```

## Demo

One composed video from `spec/popup-overlay-demo.spec.ts` — the sign-in
popup slides up over the dimmed dashboard, the cursor types the username
and password into their focused fields, clicks Sign in, the popup slides
away, and the dashboard shows the signed-in state:


https://github.com/user-attachments/assets/2e5fc8eb-b313-4cf8-8c71-f45364a07617

Deferred (noted in the task file): popup dialog annotations; child pans
degrade to plain box highlights inside the overlay.

Full suite: 142 passed. The `popups: false` path keeps the #32
standalone-video behavior, covered by the migrated specs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Session: `b7f6f792-6606-44be-9ec3-207eb762c4b6`

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>