[react] Pick the react-dom renderer instead of hardcoding renderer id 1 - #1491

Ported from vercel-labs/agent-browser vercel-labs#1491. Our react tree/inspect/suspense
scripts hardcoded rendererInterfaces.get(1); on Turbopack RSC apps (Next.js
16.3+) the react-server-dom Flight client registers first as id 1 with zero
fiber roots, so every `react` command read an empty tree. Now inject a shared
__abPickReactRendererId helper that picks the first non-Flight renderer with
mounted roots. Guarded by a unit test.

(Upstream vercel-labs#1483 wait --url globbing is already covered by our url_glob_to_regex.)

Ported from vercel-labs/agent-browser vercel-labs#1491. Our react tree/inspect/suspense
scripts hardcoded rendererInterfaces.get(1); on Turbopack RSC apps (Next.js
16.3+) the react-server-dom Flight client registers first as id 1 with zero
fiber roots, so every `react` command read an empty tree. Now inject a shared
__abPickReactRendererId helper that picks the first non-Flight renderer with
mounted roots. Guarded by a unit test.

(Upstream vercel-labs#1483 wait --url globbing is already covered by our url_glob_to_regex.)

…ercel-labs#1491)

`react tree`, `react inspect`, and `react suspense` read
`hook.rendererInterfaces.get(1)`, assuming the first renderer to call
`hook.inject()` is react-dom. In Turbopack RSC apps (e.g. Next.js 16.3+)
the `react-server-dom-turbopack` Flight client registers first as id 1
with zero fiber roots, so `get(1)` walked an empty interface and every
command silently reported nothing (`react suspense` -> "0 boundaries",
`react tree` -> empty).

Introduce a shared `__abPickReactRendererId` helper, injected via a
`{{PICK_RI}}` placeholder, that selects the first non-Flight renderer
with mounted fiber roots (falling back to any renderer with roots, then
any renderer). Use the chosen id for `inspectElement` as well.

Add unit tests asserting the scripts inject the picker and no longer
hardcode renderer id 1.