Website service Makefile and Localization package fixes (#12)

This PR contains the work done to get the Website service building and running correctly in its Linux container. The service depends on the local _Localization_ package, whose String-Catalog localization was Darwin-only and broke the Docker build. Thus the localization internals have been reworked to be platform-agnostic and fixes the container build context so the local package is actually available during the build.

* Localization package
  * Replaced the Darwin-only `String.LocalizationValue` / `String(localized:)` path with a StringCatalog type that reads raw JSON from a given `.xcstrings` file, so lookups resolve identically on macOS and Linux.
  * The `LanguageList` now derives available languages from the catalog instead of `Bundle.localizations`
  * The `Negotiate` does explicit _Accept-Language_ matching (exact tag, then primary subtag) instead of the Linux-broken `Bundle.preferredLocalizations`.
  * Switched the catalog resource rule from `.process` to `.copy` (in both Localization and Website manifests) so the raw `.xcstrings` ships verbatim on every platform.
  * Introduced a `CatalogResolving` protocol as a seam between the localizers and the storage backend, enabling test injection and a future native-Apple backend without changing callers.

* Website Docker build
  * Build context moved to the repository root so the relative-path `Localization` package is inside the context; `Dockerfile`, `docker-compose.override.yml`, and the _img-release_ make target updated to the new context/paths.
  *  Added a root `.dockerignore` to keep the context lean.

Reviewed-on: rock-n-code/loud-amsterdam#12
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Packages/Localization/Package.swift

@@ -30,7 +30,9 @@ let package = Package(
             ],
             path: "Tests",
             resources: [
-                .process("Catalogs/Localizable.xcstrings")
+                // Copied verbatim rather than processed: the String Catalog is read as raw JSON at runtime so it
+                // resolves identically on Darwin and Linux (which cannot compile it).
+                .copy("Catalogs/Localizable.xcstrings")
             ]
         ),
     ]