Replace LocalStack with Floci in test suite; add pathStyleAccess S3 setting

[Copilot]

LocalStack community edition was sunset in March 2026 (auth token required, security updates frozen). Replaces it with Floci — a free MIT-licensed drop-in alternative (~90 MB image, ~24 ms startup).

Changes

• build.gradle.kts: Remove org.testcontainers:localstack and com.amazonaws:aws-java-sdk-s3 (v1 SDK was only a transitive dep of the localstack testcontainers module)
• S3StorageProviderSettings: Add pathStyleAccess: Boolean = false — configurable per-repository, backward compatible
• S3StorageProviderFactory: Honour settings.pathStyleAccess alongside the existing reposilite.s3.pathStyleAccessEnabled JVM property
• Integration tests: Swap LocalStackContainer for GenericContainer("hectorvent/floci:latest") on port 4566 with pathStyleAccess = true (Floci, like all local S3 emulators, requires path-style access)

// Before
val localstack: LocalStackContainer = LocalStackContainer(DockerImageName.parse("localstack/localstack:latest"))
    .withServices(S3)
// credentials sourced from localstack.accessKey / .secretKey / .region

// After
val floci: GenericContainer<*> = GenericContainer(DockerImageName.parse("hectorvent/floci:latest"))
    .withExposedPorts(4566)
// S3StorageProviderSettings(endpoint = "http://${floci.host}:${floci.getMappedPort(4566)}", pathStyleAccess = true, ...)

The new pathStyleAccess setting also benefits production users running MinIO, Ceph, or similar self-hosted S3-compatible backends that require path-style URLs.

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