Remove dead code and stale configuration (#540)

[maltehuebner]

Removes the belegten dead code and orphaned configuration from #540. The Provider subsystem was already removed on main in #507, so that task is done.

Changes

Dead PHP (grep-verified: zero usages)

• src/Air/ImportCache/{ImportCache,ImportCacheInterface}.php
• src/Air/Util/ClassUtil.php, src/Air/Util/StringUtil.php
• src/Twig/Extension/CronTwigExtension.php — references Cron\CronExpression, but dragonmantank/cron-expression is not installed and the cron() Twig function is called in no template (first use would fatal)
• dropped the unused use App\Entity\Zip; import in RequestConverter (the Zip entity does not exist)

Stale configuration

• config/services.yaml: removed the unused locale parameter, the consumer-less $graphCacheDirectory bind (plus GRAPH_CACHE_DIRECTORY in .env/.env.test), and the dead alias targeting the non-existent App\Air\Pollution\DataPersister namespace. The live persister interface (App\Air\DataPersister\PersisterInterface) is the one actually injected; the old FQCN is referenced in zero use statements, so the alias was inert (Symfony drops unused private aliases).
• deleted config/packages/dev/easy_log_handler.yaml (registers EasyCorp\EasyLog\EasyLogHandler; the package is not installed and abandoned since 2020)
• removed the controller-less logout route from config/routing/4_frontend.yaml (there is no security firewall, and the route name is referenced nowhere)
• removed /phpunit.xml from .gitignore (the file is git-tracked and consumed directly by CI — the ignore line was a foot-gun)
• fixed the Kohlemnonooxid → Kohlenmonoxid keyword typo in sonata_seo.yaml

Docs

• CLAUDE.md / README.md: corrected the search description — the app has no Elasticsearch integration (zero references in composer.json/src/); search/autocomplete is client-side @algolia/autocomplete-js + Nominatim geocoding, not "Elasticsearch"/"Typeahead/Bloodhound".

Notes / deferred

• The elasticsearch service still present in docker-compose.yml (and docker/elasticsearch/) is a legacy remnant; removing the infra service/volume is out of scope for this docs+dead-code cleanup and is noted inline in CLAUDE.md.
• The locale-parameter vs translation.yaml default_locale: en inconsistency is resolved by removing the unused locale parameter.

Verification

• vendor/bin/phpstan analyse --no-progress — No errors
• vendor/bin/phpunit --testsuite="Project Test Suite" — OK (121 tests)
• All three edited YAML files parse cleanly (Symfony\Component\Yaml\Yaml::parseFile).
• Limitation: the container could not be booted here (local vendor/ lacks symfony/runtime), so the services/routing changes were verified by grep (no references to the removed ids/params/route anywhere) + YAML lint rather than a full container compile.

Refs #540 (Provider-subsystem item already done in #507)

🤖 Generated with Claude Code