Source wraps config + projectDir for build inputs.
BuildOptions consolidates all build flags with WithDefaults().

Factory interface enables pluggable build backends.
DockerfileFactory wraps existing image.Build() function.

- Resolver orchestrates building and loading Models
- Load() with functional options: LocalOnly, RemoteOnly, PreferRemote, WithPlatform
- LoadByID() for stable image ID-based lookups (short or full SHA)
- Build() delegates to Factory and inspects result
- Default PreferLocal behavior with smart fallback (only on not-found errors)
- Comprehensive tests with mocked docker/registry

Implements the Ref pattern for declarative model resolution:
- Ref interface with internal resolve() method
- TagRef/FromTag: resolves via Load (local-first, fallback to remote)
- LocalRef/FromLocal: resolves from local docker daemon only
- RemoteRef/FromRemote: resolves from remote registry only
- BuildRef/FromBuild: resolves by building from Source
- Resolver.Resolve(ctx, ref) dispatches to appropriate resolution

- ImageBuild now returns (string, error) with manifest digest
- image.Build() returns the final image ID from label-adding step
- DockerfileFactory.Build() populates Image.Digest
- Resolver.Build() uses digest for inspection, falls back to tag

This fixes instability where tag resolution could pull from remote
registry instead of using the locally-built image.

Refactor build.go to use the new model.Resolver.Build() API instead of
directly calling image.Build() with 19 parameters. This encapsulates
build complexity behind the Resolver abstraction.

Changes:
- Replace config.GetConfig() with model.NewSource()
- Replace image.Build() call with resolver.Build() using BuildOptions
- Use m.ImageRef() for output message instead of input imageName
- Add defensive nil checks for src.Config.Build

…dels

- Rename Load() to Inspect() for clearer semantics (metadata only, no pull)
- Add Pull() method that ensures image is locally available
- Add sentinel errors: ErrNotCogModel, ErrNotFound
- Validate Cog model labels in both local and remote inspection
- Update registry.Inspect() to fetch config blob for labels
- Support multi-platform indexes by picking default image for labels
- Migrate CLI commands (predict, train) to use resolver.Pull()
- Add BuildBase support for dev mode base image builds

- Add Image.ParsedConfig() - parses cog config JSON from labels
- Add Image.ParsedOpenAPISchema() - parses OpenAPI schema from labels
- Add Image.ToModel() - converts Image to Model by parsing labels
- Refactor resolver to use new methods, eliminating duplicate parsing code
- Fix: schema parsing errors now propagate instead of being swallowed

- Remove redundant inspectLocal wrapper in Pull()
- Drop unused Model fields (Weights, Runtime, GitCommit, GitTag)
- Fix pickDefaultImage to log errors instead of silently swallowing
- Deprecate Fast field in BuildOptions (read from config at build time)
- Fix test mocks to return errors instead of panic

- Pass context to pickDefaultImage for cancellation support
- Add name.Insecure option to NewDigest for HTTP registry compatibility
- Validate ImageBuild returns non-empty image ID from buildkit
- Fix comment: org.cogmodel.config -> run.cog.config
- Add nil validation to Resolver.Build/BuildBase methods