Fix Docker quickstart on homepage: missing intl, wrong bin/cake invocation, missing pdo_mysql

[Nelwhix]

Problem

Following the Docker quickstart in docs/en/index.md exactly as written fails
in three separate ways:

1. docker run -it --rm -v $(pwd):/app composer create-project ... fails
   during dependency resolution:

   cakephp/cakephp requires ext-intl * -> it is missing from your system.

2. Once a project exists, docker run ... php:8.2-cli php bin/cake server -H 0.0.0.0 doesn't start a server at all. It exits immediately with no
   error, having printed nothing useful.

3. Even after fixing both of the above, loading the welcome page returns a 500 (Cake\Database\Exception\MissingExtensionException) instead of
   the "green checkmarks" page the docs promise.

Why

1. The bare composer Docker image doesn't bundle the intl extension,
   which cakephp/cakephp requires. This is the same bug already reported in
   Can't init CakePHP with Docker solution - requires ext-intl * -> it is missing from your system. Install or enable PHP's intl extension. #8319 and fixed in Fix Docker quickstart: install intl before composer create-project #8322 — but that fix only touched
   docs/en/installation.md, not this homepage copy of the same instructions,
   so it was missed here.

2. bin/cake is a plain POSIX shell script (#!/usr/bin/env sh), not a
   polyglot PHP file. Running php bin/cake ... makes PHP treat the whole
   script as literal HTML output (no <?php tag), print its source, and
   exit 0. It needs to invoke bin/cake.php, the actual PHP entry point.

3. The scaffolded app's default config/app_local.php points at MySQL, and
   php:8.2-cli has no pdo_mysql. Without it, CakePHP's driver check
   throws before the welcome page can render its normal pass/fail checklist,
   producing a full error page instead of a graceful "problem" row.

Solution

Apply the same install-before-run pattern from #8322 to both Docker commands
on this page: run Composer inside a php:8.2-cli image with intl
installed rather than the bare composer image, install intl and
pdo_mysql before starting the dev server, and call bin/cake.php instead
of bin/cake.

Verified end to end on this patch:

• create-project scaffolds cakephp/app:~5.4 with no platform requirement
  errors (vendor/, bin/cake.php present)
• the dev server starts and responds 200 at http://localhost:8765/
• the welcome page checklist shows PHP version, mbstring, openssl, intl,
  tmp/logs writable, and DebugKit all green; only the (expected, unrelated)
  "no MySQL server running" DB check is red