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>

.github/workflows/go-ci.yml

@@ -36,7 +36,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v4
       with:
-        go-version: '1.23'
+        go-version-file: go.mod
 
     # Only run in this linux based runner
     - name: Check Formatting
@@ -51,7 +51,7 @@ jobs:
       uses: actions/cache/restore@v4
       with:
         path: ./build
-        key: ${{ runner.os }}-simple-responder-${{ hashFiles('misc/simple-responder/simple-responder.go') }}
+        key: ${{ runner.os }}-simple-responder-${{ hashFiles('cmd/simple-responder/simple-responder.go') }}
 
     # necessary for testing proxy/Process swapping
     - name: Create simple-responder
@@ -67,4 +67,4 @@ jobs:
         key: ${{ runner.os }}-simple-responder-${{ hashFiles('misc/simple-responder/simple-responder.go') }}
 
     - name: Test all
-      run: make test-all
+      run: make test-all