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>

.dockerignore

@@ -0,0 +1,28 @@
+# Build context is the repo root (see Services/Website/Dockerfile). Keep the
+# context lean: exclude build artifacts, VCS, IDE cruft, secrets and anything
+# not needed to compile the Swift package.
+
+# Version control
+.git
+**/.git
+
+# Swift / SPM build artifacts
+**/.build
+**/.swiftpm
+
+# Xcode project (not used by the Linux build)
+*.xcodeproj
+
+# OS / editor cruft
+**/.DS_Store
+.vscode
+
+# Local environment overrides and secrets (Compose still reads these from the
+# host at runtime; ignoring them here only keeps them out of the image build).
+**/.env
+**/.env.local
+
+# Compose / tooling / docs not needed inside the image
+**/docker-compose.*
+**/Makefile
+**/README.md