fix: stabilize public demo and align sorter twins

Document arhipovdan.ru DNS/TLS blocker, add production smoke and GPU
perf tooling, unify twin layout, and expand visual regression coverage.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/HEADED_GPU_PERFORMANCE_REPORT.md

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+# HEADED_GPU_PERFORMANCE_REPORT
+
+Measured: 2026-07-15T17:48:54.064Z
+Commit: `b5985f3`
+Base URL: http://127.0.0.1:3101/
+Display: headed (:99)
+Software renderer detected: **YES**
+Verdict: **NOT A GPU BASELINE — software renderer (SwiftShader/llvmpipe/etc.)**
+
+## Notes
+
+- Headed Chromium with GPU-preferring flags.
+- PerfCollector only with `?perf=1`; quality forced via `?quality=`.
+- Prior headless ~9.6 FPS is labeled software/headless WebGL diagnostic baseline.
+- **Host has NVIDIA GTX 1080 ×2**, but Playwright Chromium in this coder/Xvfb session resolves WebGL to **SwiftShader** — numbers below are **not** a hardware GPU baseline.
+- For true GPU baseline: run `PLAYWRIGHT_BASE_URL=… npm run perf:gpu` on the presentation machine with a real `DISPLAY` and confirm renderer does **not** contain SwiftShader/llvmpipe.
+
+## Mode table (after Play)
+
+| Mode | Renderer | Avg FPS | Min FPS | p95 | Calls | Triangles | Heap |
+| ---- | -------- | ------: | ------: | --: | ----: | --------: | ---: |
+| low | ANGLE (Google, Vulkan 1.3.0 (SwiftShader Device (Subzero) (0x0000C0DE)), SwiftShader driver) | 10.58 | 4.44 | 151.9 | 167 | 3546 | 16.26 |
+| medium | ANGLE (Google, Vulkan 1.3.0 (SwiftShader Device (Subzero) (0x0000C0DE)), SwiftShader driver) | 9.91 | 4.68 | 158.28 | 167 | 3546 | 16.38 |
+| high | ANGLE (Google, Vulkan 1.3.0 (SwiftShader Device (Subzero) (0x0000C0DE)), SwiftShader driver) | 8.69 | 4.03 | 182.2 | 167 | 3546 | 17.45 |
+| demo | ANGLE (Google, Vulkan 1.3.0 (SwiftShader Device (Subzero) (0x0000C0DE)), SwiftShader driver) | 8.88 | 4.17 | 181.81 | 167 | 3546 | 21.1 |
+
+## Memory after 3 seek+replay (demo mode)
+
+```
+{
+  "heapDeltaMb": 2.19,
+  "geometriesDelta": 12,
+  "texturesDelta": 0
+}
+```
+
+## Prior software/headless WebGL diagnostic baseline (reference only)
+
+```
+Average FPS: 9.6
+Minimum FPS: 3.3
+p95 frame time: 200 ms
+```
+
+Do **not** treat the above as live-demo GPU characteristics.
+
+## Chromium launch args
+
+```
+--use-gl=angle --use-angle=gl-egl --enable-webgl --enable-webgl2 --ignore-gpu-blocklist --enable-gpu-rasterization --enable-precise-memory-info --enable-unsafe-swiftshader
+```
+
+Raw JSON: `agent/reports/gpu-baseline.json`