docs: document routePriority and CSP nonce (5.0)

[soyuka]

Summary

• Documents routePriority (core#8309, corrected by core#8529) in core/operations.md: an operation-level option that controls Symfony route matching order, with a worked example of a static /books/featured route colliding with /books/{id}. Explicitly disambiguated from the pre-existing priority option, which sorts in the opposite direction and serves a different purpose (operation-list ordering, e.g. IRI generation) — the two were split in #8529 specifically because #8309 initially reused priority for routing.
• Documents the CSP nonce support on Swagger UI (core/openapi.md) and GraphiQL (core/graphql.md) added in core#8310, cross-linking the two sections instead of duplicating the explanation. Precedence confirmed against tests/Functional/SwaggerUiCspNonceTest.php and tests/Functional/GraphQl/GraphiqlCspNonceTest.php: the _csp_nonce request attribute wins over a Twig csp_nonce() function (e.g. NelmioSecurityBundle), and if neither is present no nonce attribute is emitted. Both features are Symfony-only on main (verified: src/Symfony/Bundle/SwaggerUi/SwaggerUiProcessor.php and the Symfony-registered GraphiQlAction; Laravel's Swagger/GraphiQL views are untouched by core#8310).

Both features are 5.0-only (main); verified absent from upstream/4.4.

Test plan

• npx prettier@3.9.5 --check on the three touched files passes (whole-repo check shows only pre-existing, unrelated failures in core/doctrine-filters.md / core/filters.md, files not touched by this PR)
• Claims verified against api-platform/core upstream/main source (src/Metadata/Operation.php, src/Symfony/Routing/ApiLoader.php, vendor/symfony/routing/RouteCollection.php, src/GraphQl/Action/GraphiQlAction.php, src/Symfony/Bundle/SwaggerUi/SwaggerUiProcessor.php)