proxy, ui-svelte: add /sdapi/v1 endpoint support (#587)

Add proxy routes for stable-diffusion.cpp's /sdapi/v1/txt2img,
/sdapi/v1/img2img, and /sdapi/v1/loras endpoints. POST endpoints
use proxyInferenceHandler (model in JSON body), GET /loras uses
proxyGETModelHandler (model in query param).

Update the image playground with a dual-mode UI supporting both
OpenAI and SDAPI backends. In SDAPI mode, loras are fetched first
to prime the server-side cache, and all txt2img parameters are
exposed (negative prompt, steps, cfg_scale, seed, batch_size,
clip_skip, sampler, scheduler, lora selection with multipliers).

- Add 3 sdapi route registrations in proxymanager.go
- Add sdApi.ts client with generateSdImage and fetchSdLoras
- Add SDAPI types (SdApiTxt2ImgRequest, SdApiResponse, etc.)
- Add /sdapi to vite dev proxy config
- Add backend tests for sdapi routing
- Support batch image display in gallery grid

https://claude.ai/code/session_0186MGX6NXdHVBTv2KH45fqn

---------

Co-authored-by: Claude <noreply@anthropic.com>

ui-svelte/src/lib/sdApi.ts

@@ -0,0 +1,39 @@
+import type { SdApiTxt2ImgRequest, SdApiResponse, SdApiLora } from "./types";
+
+export async function generateSdImage(
+  request: SdApiTxt2ImgRequest,
+  signal?: AbortSignal
+): Promise<SdApiResponse> {
+  const response = await fetch("/sdapi/v1/txt2img", {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/json",
+    },
+    body: JSON.stringify(request),
+    signal,
+  });
+
+  if (!response.ok) {
+    const errorText = await response.text();
+    throw new Error(`SDAPI error: ${response.status} - ${errorText}`);
+  }
+
+  return response.json();
+}
+
+export async function fetchSdLoras(
+  model: string,
+  signal?: AbortSignal
+): Promise<SdApiLora[]> {
+  const response = await fetch(
+    `/sdapi/v1/loras?model=${encodeURIComponent(model)}`,
+    { signal }
+  );
+
+  if (!response.ok) {
+    const errorText = await response.text();
+    throw new Error(`SDAPI loras error: ${response.status} - ${errorText}`);
+  }
+
+  return response.json();
+}

ui-svelte/src/lib/types.ts

@@ -115,6 +115,40 @@ export interface ImageGenerationResponse {
   }>;
 }
 
+// SDAPI types (stable-diffusion.cpp)
+export type ImageApiMode = "openai" | "sdapi";
+
+export interface SdApiLora {
+  name: string;
+  path: string;
+}
+
+export interface SdApiLoraRef {
+  path: string;
+  multiplier: number;
+}
+
+export interface SdApiTxt2ImgRequest {
+  model?: string;
+  prompt: string;
+  negative_prompt?: string;
+  width?: number;
+  height?: number;
+  steps?: number;
+  cfg_scale?: number;
+  seed?: number;
+  batch_size?: number;
+  sampler_name?: string;
+  scheduler?: string;
+  lora?: SdApiLoraRef[];
+}
+
+export interface SdApiResponse {
+  images: string[];
+  parameters: Record<string, unknown>;
+  info: string;
+}
+
 export interface AudioTranscriptionRequest {
   file: File;
   model: string;