Add a `proxy mirror` CLI command and `/api/mirror` API endpoints that
pre-populate the cache from various input sources: individual PURLs,
SBOM files (CycloneDX and SPDX), or full registry enumeration.
The mirror reuses the existing handler.Proxy.GetOrFetchArtifact()
pipeline so cached artifacts are identical to those fetched on demand.
A bounded worker pool controls download parallelism.
Metadata caching is opt-in via `cache_metadata: true` in config (or
PROXY_CACHE_METADATA=true). The mirror command always enables it. When
enabled, upstream metadata responses are stored for offline fallback
with ETag-based conditional revalidation.
New internal/mirror package with Source interface, PURLSource,
SBOMSource, RegistrySource, and async JobStore. New metadata_cache
database table for offline metadata serving.
* Fix all golangci-lint issues across the codebase
Resolve 77 lint issues reported by golangci-lint with gocritic, gocognit,
gocyclo, maintidx, dupl, mnd, unparam, ireturn, goconst, and errcheck
enabled. Net reduction of ~175 lines through shared helpers and
deduplication.
* Suppress staticcheck SA1019 for intentional deprecated field usage
The Storage.Path field is deprecated but still read for backwards
compatibility with existing configs that haven't migrated to the URL field.
All handler metadata and proxy requests were using http.DefaultClient directly,
bypassing any timeout or transport configuration. Added an HTTPClient field to
the Proxy struct with a 30-second default timeout, and updated every handler
to use it for upstream HTTP requests.
