feat: wave-3 image + document surfaces — segmentation, colorize, face restore, ocr (ADR-0023)

- imagegen.Segmenter/SegmentationProvider: prompted mask via
  POST /upstream/<id>/v1/segment (file, prompt[, threshold], output=mask);
  white = prompted region, EditRequest.Mask polarity.
- imagegen.Colorizer/ColorizeProvider: POST /upstream/<id>/v1/colorize.
- imagegen.FaceRestorer/FaceRestoreProvider:
  POST /upstream/<id>/v1/restore_faces (upscale 1|2).
- New ocr leaf package (Request/Page/Result, Recognize) + llamaswap
  OCRModel: POST /upstream/<id>/v1/ocr (file[, langs, max_pages]),
  tolerant per-page decode (join lines when page text absent), Raw
  escape hatch.
- httptest contract tests per surface; ADR-0023; ADR index backfilled
  (0020-0022 rows were missing).

Co-Authored-By: Claude Fable 5 <[email protected]>

imagegen/colorize.go

@@ -0,0 +1,54 @@
+package imagegen
+
+import "context"
+
+// ColorizeRequest asks a colorization backend (DDColor style) to add color to
+// a grayscale/faded photo (ADR-0023).
+type ColorizeRequest struct {
+	// Image is the image to colorize. Required.
+	Image Image
+}
+
+// ColorizeOption mutates a ColorizeRequest before it is sent. Reserved for
+// future request settings (the reference backend takes no parameters).
+type ColorizeOption func(*ColorizeRequest)
+
+// Apply returns a copy of the request with all options applied.
+func (r ColorizeRequest) Apply(opts ...ColorizeOption) ColorizeRequest {
+	for _, opt := range opts {
+		opt(&r)
+	}
+	return r
+}
+
+// Colorizer adds color to grayscale images.
+type Colorizer interface {
+	// Colorize returns the colorized image as a one-image Result.
+	Colorize(ctx context.Context, req ColorizeRequest, opts ...ColorizeOption) (*Result, error)
+}
+
+// ColorizeModelOption configures a Colorizer at construction time. Reserved
+// for future per-model settings.
+type ColorizeModelOption func(*ColorizeModelConfig)
+
+// ColorizeModelConfig carries per-model construction settings.
+type ColorizeModelConfig struct{}
+
+// ApplyColorizeModelOptions folds options into a config.
+func ApplyColorizeModelOptions(opts []ColorizeModelOption) ColorizeModelConfig {
+	var cfg ColorizeModelConfig
+	for _, opt := range opts {
+		opt(&cfg)
+	}
+	return cfg
+}
+
+// ColorizeProvider mints Colorizers bound to one backend.
+type ColorizeProvider interface {
+	// Name is the registry identifier for the provider.
+	Name() string
+
+	// ColorizeModel returns a Colorizer bound to the given id (passed through
+	// to the backend verbatim; no catalog validation).
+	ColorizeModel(id string, opts ...ColorizeModelOption) (Colorizer, error)
+}