Parse environment variables in the bucket setting

[jmariklecr]

Description

On 3.x, the bucket setting isn't run through Env::parse() in getDiskConfig(), so an env var reference reaches the S3 client verbatim. With bucket: $S3_BUCKET in project config, every operation fails:

Error executing "HeadObject" on
"https://s3.amazonaws.com/%24S3_BUCKET/general-uploads/placeholders/100x100-1.jpg";
AWS HTTP error: 400 Bad Request

(%24S3_BUCKET being the URL-encoded literal $S3_BUCKET.)

A regression from the 6.x port. On 2.x, env parsing was declarative via EnvAttributeParserBehavior, covering seven attributes: keyId, secret, bucket, region, subfolder, cfDistributionId, cfPrefix. That behavior went away in the rewrite and each attribute became an explicit Env::parse() call. Six of seven were converted, bucket was missed.

This should be a safe change. The same Env::parse is used further down the same file:

aws-s3/src/Filesystems/S3.php

Lines 368 to 375 in 861201f

	$params = [
	'Image' => [
	'S3Object' => [
	'Name' => $path,
	'Bucket' => Env::parse($this->bucket),
	],
	],
	];

Related issues

None. #181 is Craft 4 and unrelated. 2.x isn't affected (still uses the behavior).

Note on verification / CI

The 3.x branch's tooling doesn't appear to have been updated during the port, so
neither phpstan nor ECS run cleanly.

• composer install fails: composer.lock still pins craftcms/cms 4.17.7 while composer.json requires ^6.0.0 (composer update resolves cleanly to 6.0.0-alpha.16. I did not include the resulting composer.lock in this PR)
• composer phpstan fails: phpstan.neon includes craftcms/phpstan's shared config, which scans ../cms/src/Craft.php. That file doesn't exist in Craft 6. The legacy Craft class now lives in craftcms/yii2-adapter, which this plugin doesn't require, so PHPStan can't run on this branch at all.
• composer check-cs exits 1 with 7 pre-existing violations across the branch, none related to this change. I decided not to fix them considering they are unrelated to the current work.
• .github/workflows/ci.yml still specifies craft_version: '5' / php_version: '8.1'

The change itself was verified manually on Craft 6.0.0-alpha.16 / PHP 8.5: with bucket set via $S3_BUCKET, S3 operations return 400 before and succeed after. fileExists() true, correct size(), and the CP Assets index browses the volume.

Tooling issues probably belong in a separate PR.

Addendum

I used Claude Code to diagnose the issue and specifically checked whether it was isolated. bucket in getDiskConfig() appears to be the only one missing Env::parse().