feat: indicate whether an extension pack/dependency reference is available

[netomi]

Closes #224.

What

Extension packs have not required their bundled extensions to already exist in the registry for some time now: bundledExtensions is stored as a plain list of namespace.extension strings, and publish-time validation only checks the format, not resolvability - unlike extensionDependencies, which does still check resolvability. So the core ask in #224 (publish a pack referencing extensions that aren't yet published here) has worked for a while.

What was still missing, per the later discussion on that issue: the API handed back a URL for every bundled-extension/dependency reference whether or not it actually resolved, and the extension detail page linked to all of them uniformly - following a reference to an unpublished (or since-removed) extension led to a bare 404 with no indication beforehand.

Changes

• Server: ExtensionReferenceJson gains an available boolean. LocalRegistryService.resolveExtensionReferences (renamed from setExtensionReferenceUrls, made package-private so it can be tested directly) sets it via repositories.findActiveExtension(...) for every bundled-extension/dependency reference, alongside the URL it already set.
• webui: ExtensionReference.available (optional, so older registries that don't send this field yet are treated as available - no behavior change for them). The extension detail page's renderExtensionRef now shows an unavailable reference as plain namespace.extension (not available) text instead of a dead link.

Testing

• LocalRegistryServiceTest: 2 new tests covering an available reference, an unavailable one, and the null-list no-op case.
• extension-detail-overview.spec.tsx (new file): 4 tests covering both bundled extensions and dependencies, available and unavailable.

Server: ./gradlew test - 1054/1054 passing. Webui: yarn lint clean, yarn test - 171/171 passing.

[netomi]

Pushed a follow-up commit addressing two related cache/availability gaps found while reviewing this change:

1. Cache invalidation: extension.json was only evicted for the extension that changed, not for other extensions that reference it as a bundled extension/dependency. So if extension A bundles B, and A's json gets cached before B is published, publishing B afterwards never invalidated A's cache — it kept reporting available: false for B. ExtensionService.updateExtension (the single choke point already invoked whenever an extension's active status changes) now also evicts the cache of every referencing extension, reusing the existing RepositoryService.findBundledExtensionsReference/findDependenciesReference queries.

2. v1 API gap: resolveExtensionReferences (which sets the available flag) had only been wired into toExtensionVersionJsonV2. The two v1 toExtensionVersionJson overloads — backing the v1 getExtension/query endpoints and the publish response — still used their own older logic that set the URL but never available. Both now delegate to resolveExtensionReferences like v2 does.

Added regression tests for both (ExtensionServiceTest, LocalRegistryServiceTest) and fixed a couple of pre-existing test mocks that needed the newly-called repository methods stubbed. Full ./gradlew test run: 1057/1057 passing.

[netomi]

Actually I am not sure anymore if this is really worth it.