fix: QA sweep -- SSE crash, memory leaks, HEIC Docker decode, TGA detection, lint cleanup

- Fix SSE write-after-end crash in progress.ts (remove callback before ending stream)
- Fix blob URL memory leaks: revoke processedPreviewUrl and old HEIC preview URLs
- Add AbortController to batch fetch in use-tool-processor and use-pipeline-processor
- Fix TGA format misidentified as CUR (extension overrides magic bytes)
- Add libheif-plugin-libde265 to Docker for HEIC/HEIF decode support
- Remove unused imports and state (AppLayout, setSampledColor, useEffect)
- Fix non-null assertions in meme-text-renderer and meme-generator
- Fix confusing void type in meme-templates
- Remove unnecessary useEffect deps in adjustments-panel
- Fix Playwright strict mode violations in 5 E2E tests

docker/Dockerfile.test

@@ -12,6 +12,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libimage-exiftool-perl \
     imagemagick \
     libraw-dev \
+    && if apt-cache show libheif-plugin-libde265 >/dev/null 2>&1; then \
+         apt-get install -y --no-install-recommends libheif-plugin-libde265; \
+       fi \
     && if apt-cache show libheif-plugin-x265 >/dev/null 2>&1; then \
          apt-get install -y --no-install-recommends libheif-plugin-x265; \
        fi \