wp-env environment: EOL PHP 7.4 and unpinned Gutenberg trunk don't match what learners actually run

Problem

.wp-env.json defines the environment every contributor (and future CI) develops and tests in, and it diverges from what users of these examples actually run:

• "phpVersion": "7.4" — EOL since November 2022. Examples are developed and tested on a PHP version WordPress hosting recommendations have moved past; PHP 8.x deprecation warnings that learners would hit ship unseen.
• The Gutenberg plugin is installed from an unpinned trunk zip (https://downloads.wordpress.org/plugin/gutenberg.zip). Every API these examples demonstrate — including the Interactivity API and its router — is in stable core now, so the dev/test environment runs different editor code than a stock WordPress site, and a non-deterministic version of it at that.

Proposed fix

1. Bump phpVersion to 8.2 (current WordPress hosting recommendation).
2. Remove the Gutenberg plugin from .wp-env.json. If a future example genuinely needs a Gutenberg-plugin-only feature, add it back deliberately — pinned — and note the requirement in that example's README.
3. Leave core unpinned (latest stable): an examples repo should break loudly when a new WordPress release breaks an example, and per-PR e2e (#147) makes that visible quickly.

Consequences to be aware of

• Examples will no longer be exercised against upcoming editor features ahead of core releases — accepted trade-off; matching the learner's environment wins.
• Most plugin headers claim Requires PHP: 7.0 while the repo will only test on 8.2. The header-normalization PR in #150 should align those claims with what is actually tested.

Out of scope

• .nvmrc pinning and packageManager (covered by #148).
• Plugin header Requires corrections (covered by #150).

Start with .wp-env.json and compare its phpVersion, Gutenberg plugin URL, and core settings with the proposed environment. Update the environment to PHP 8.2 without Gutenberg, then run the per-PR e2e checks referenced in #147 and confirm the examples still work against latest stable core.