Add Redirect rules MVP via EventSubscriber (KernelEvents::REQUEST) with config UI and caching

Problem/Motivation MyREST SEO lacks a built‑in way to define simple SEO redirects (301/302). A small native feature for common redirect rules (old → new paths) would help small sites without installing Redirect. Must not conflict with Redirect if present.
Proposed resolution
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Implement an EventSubscriber on KernelEvents::REQUEST with early priority to apply configured redirects before controller resolution.
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Add a config UI at /admin/seo/redirects to manage rules (source, target, 301/302, enabled; optional regex; optional language/site contexts).
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Add proper cacheability: contexts (languages:language_interface, url.path), tags (config:myrest_seo.redirects), and safe short‑circuiting only on match.
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Compatibility: if Redirect module is enabled, our subscriber is disabled by default (toggle in settings).
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Tests: finish/extend the current routes functional test and add Kernel/Functional tests for redirect behavior.
Tasks
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[ ] Config schema: myrest_seo.redirects (rule list) and myrest_seo.settings.redirects_enabled.
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[ ] EventSubscriber: src/EventSubscriber/RedirectSubscriber.php applying redirects.
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[ ] Admin form: src/Form/RedirectsForm.php at /admin/seo/redirects (permission: administer myrest_seo; _admin_route: TRUE).
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[ ] Cacheability: add contexts/tags; ensure no cache poisoning.
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[ ] Tests: Kernel test for matcher; Functional test verifying 301/302 redirect and that feature can be toggled; ensure no conflict when Redirect module is present.
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[ ] Docs: README section (feature + coexistence note).
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[ ] CI stays green (PHPCS, phpstan‑drupal, PHPUnit).
Acceptance criteria
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[ ] Rules are editable via /admin/seo/redirects and stored in exportable config.
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[ ] Matching requests return correct 301/302 to target.
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[ ] With Redirect module enabled and the toggle off, no duplicate redirects occur.
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[ ] Tests green on drupal.org CI; PHPCS/phpstan‑drupal pass.
Testing instructions
1)
Create /old → /new (301); visit /old → expect 301 to /new.
2)
Disable the feature; /old should no longer redirect.
3)
Enable Redirect module; confirm our subscriber is disabled (no duplication).