feat(api): add OpenAI compatibility for image models

- Introduced OpenAI-compatible image model support in the API, enabling integration through image generation and editing endpoints.
- Added registry type for OpenAIImageModelType to classify and validate compatibility.
- Implemented request handling for OpenAI-compatible image models, including JSON and multipart formats.
- Enhanced executor methods to support OpenAI-compatible image streaming and non-streaming requests.
- Included tests to validate model registration, streaming behavior, and multipart payload formatting.

internal/watcher/diff/model_hash.go

@@ -4,6 +4,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"sort"
 	"strings"
 
@@ -20,7 +21,7 @@ func ComputeOpenAICompatModelsHash(models []config.OpenAICompatibilityModel) str
 			if name == "" && alias == "" {
 				continue
 			}
-			out(strings.ToLower(name) + "|" + strings.ToLower(alias))
+			out(strings.ToLower(name) + "|" + strings.ToLower(alias) + "|" + fmt.Sprintf("image=%t", model.Image))
 		}
 	})
 	return hashJoined(keys)