refactor: use the 8.3 features that carry weight

[refsz]

Follow-up to #33, kept separate so the version bump stays mechanical. Merge #33 first; GitHub retargets this to main.

Two changes, both with a reason beyond "8.3 allows it":

The typed class constant comes back. private const array DEFAULT_SHELL in EnvironmentDetector had to lose its type under 8.2, with PHPStan naming the reason.

#[Override] on the redacting decorators. This is not decoration. The masking leak found earlier today was exactly a method that no longer matched its parent: ConsoleSectionOutput::overwrite() takes a cursor-rewind path on a decorated terminal that writes via doWrite() directly, bypassing the write() and writeln() overrides — and nothing failed, output just quietly stopped being redacted. I found it by reading Symfony's source, which is not a strategy.

With the attribute, a renamed or resignatured parent method is a fatal error at load time:

PHP Fatal error: Sputnik\Secret\RedactingConsoleSectionOutput::overwriteTypo()
has #[\Override] attribute, but no matching parent method exists

That output is from actually renaming one override and watching the class refuse to load, then reverting. It is the cheapest possible guard on the six methods where a silent mismatch means a secret reaches the terminal.

Deliberately not included

• Typing every existing constant. PHPStan already infers precise types from literals, so a sweep would change 12 files for style alone.
• Rewriting withFormatter() as a clone. I claimed in build!: require PHP 8.3 #33 that 8.3 makes this possible and then checked it: readonly properties may be reinitialised only inside __clone(), which cannot receive the new value. Outside it, PHP still throws Cannot modify readonly property. The existing new self(...) is correct and stays.

Verification

vendor/bin/phpunit          742 tests, 1281 assertions, OK
vendor/bin/phpstan analyse  [OK] No errors
vendor/bin/php-cs-fixer     0 of 153 files
vendor/bin/rector --dry-run [OK]

🤖 Generated with Claude Code

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