feat(gui): source brand marks for 23 providers that rendered a letter tile

The provider rail, details panel and dashboard rows fall back to a coloured
initial tile when providerIconSrc returns nothing, which was 38 of 83 registry
providers. This sources marks for 23 of them.

Eleven vendors publish a usable square SVG and are committed as fetched, with
only comments, <title>/<desc> and data-name stripped. Twelve publish no square
vector, so their favicon or app icon is traced -- potrace for a single-ink
silhouette, k-means colour layers for multi-colour art, the same technique that
produced hermes-agent.svg and gajae-code.svg.

The first tracing pass shipped a bug worth recording. A favicon is usually a
glyph on a filled rounded square, and tracing by luminance captured the square:
baseten came out 97.7% ink, bizrouter 89.3% -- black boxes, not marks. The fix
reads the border ring, takes its median colour as the plate when the ring is
uniform, and masks by distance from that colour rather than by darkness. It found
real plates behind baseten (#19e76e), cerebras (#ef5b27), hyperbolic (#1a1a1a),
umans and bizrouter (#000000), and orcarouter (#ffffff).

Two candidates were rejected rather than shipped. nousresearch.com publishes only
safari-pinned-tab.svg, whose first path is the full 512-unit frame -- the exact
file the Hermes client mark rejected for rendering as a black square. LiteLLM has
no mark of its own on its site; the SVGs there are third-party model logos. Both
keep their fallback tile with the attempt recorded.

Two guards. One fails a mark that passes an SVG parse but is a <text> glyph, an
embedded raster or a base64 payload -- none of which is visible in review and all
of which break in a 19px box. The other fails a horizontal wordmark by viewBox
ratio, which is what disqualified six vendor logos here and the MiniMax docs
asset in the previous unit.

Providers with no resolved mark: 38 -> 15 on this branch.

Measured after: 18 of the 23 fall under 2:1 against one of the two surfaces,
because ProviderIcon has no themed path at all. That is wp5, not a defect in
these assets.

Verification: 2 pass in the new file, each driven red (a text glyph, a 5.1:1
lockup). tsc 0 both roots, oxlint clean, privacy:scan clean, full GUI suite 1156
pass / 0 fail across 187 files. Every mark rendered at 19px in the real tile in
both themes with no load failures.

Author: lidge-jun

gui/public/provider-icons/README.md

@@ -140,3 +140,63 @@ Both directions are enforced in `gui/tests/integration-marks.test.ts`, including
 luminance check that fails any single-ink near-neutral mark left as an image. That
 direction was missing until it caught `grok`; the same class of defect had already
 shipped once for `prime`, `opencode` and `kimi`.
+
+## Provider marks (2026-09-01)
+
+Sourced for the providers that were rendering a coloured initial tile. Every
+entry below was fetched from the vendor's own domain, taken from the registry's
+`baseUrl`/`dashboardUrl` rather than guessed.
+
+Published as SVG and committed with only comments, `<title>`/`<desc>` and
+`data-name` attributes stripped:
+
+- `digitalocean.svg` — `digitalocean.com` favicon, 32x32.
+- `featherless.svg` — `featherless.ai/favicon.svg`, 256x256.
+- `kilo.svg` — `kilo.ai/favicon/favicon.svg`, 32x32. Keeps its `oklch()` plate.
+- `nanogpt.svg` — `nano-gpt.com/logo.svg`, 181x187, gradient.
+- `nebius.svg` — `nebius.com/favicon/favicon.svg`, 96x96.
+- `neuralwatt.svg` — the site's Webflow-hosted brand asset, 32x32.
+- `parallel.svg` — `parallel.ai/icon.svg`, 96x96.
+- `scaleway.svg` — `scaleway.com/favicon/website/favicon.svg`, 16x16.
+- `synthetic.svg` — `synthetic.new/favicon.svg`, 54x54.
+- `zai.svg` — `z-cdn.chatglm.cn/z-ai/static/logo.svg`, 30x30.
+- `zenmux.svg` — the site's CDN-hosted brand mark, 160x160.
+
+Traced from raster, because the vendor publishes no square SVG mark. Same
+technique as `hermes-agent.svg` and `gajae-code.svg`: `potrace -s --flat` for a
+single-ink silhouette, k-means colour layers (seeded at 3, largest area first)
+for multi-colour art, downsampled to a 160px box first so the trace does not
+follow every upscaled pixel edge.
+
+- `cerebras.svg`, `novita.svg`, `siliconflow.svg`, `deepinfra.svg` — single-ink.
+- `baseten.svg`, `hyperbolic.svg`, `sambanova.svg`, `umans.svg`, `venice.svg`,
+  `vultr.svg`, `bizrouter.svg`, `orcarouter.svg` — colour-layered.
+
+**The plate problem, recorded because the first pass shipped it.** A favicon is
+usually a glyph on a filled rounded square. Tracing luminance alone captured the
+square and produced a solid box: `baseten` came out 97.7% ink, `bizrouter` 89.3%.
+The fix reads the border ring, takes its median colour as the plate when the ring
+is uniform, and masks by distance from that colour instead of by darkness. It
+found real plates behind `baseten` (#19e76e), `cerebras` (#ef5b27), `hyperbolic`
+(#1a1a1a), `umans`/`bizrouter` (#000000) and `orcarouter` (#ffffff).
+
+### Rejected, and why
+
+- **`nous`** — `nousresearch.com/safari-pinned-tab.svg` opens with the full
+  512-unit frame as its first path, so it renders as a black square. This is the
+  identical candidate the Hermes client mark rejected. Nous Research keeps its
+  fallback tile; reusing `hermes-agent.svg` would attribute a product's mark to
+  its publisher.
+- **`litellm`** — the traced favicon is a muddy multi-colour blob with no legible
+  silhouette at 19px. The homepage SVGs are third-party model logos, not LiteLLM's
+  own mark.
+- **Wordmarks refused** for `cerebras` (843x320 from Sanity CDN), `siliconflow`
+  (188x28), `zhipu-bigmodel` (123x25), `vultr` (218x52), `baseten` (1001x151) and
+  `chutes` (192x30). A lockup in the rail's 19px box is an illegible smear, so
+  each was replaced by a traced square mark or left to the fallback.
+- **Nothing found** for `chutes`, `nscale`, `together`, `volcengine` and
+  `tencent-coding-plan`: no square SVG and no usable raster icon at the
+  registry's domains. They keep their fallback tiles.
+
+`zhipu-bigmodel` and `zhipu-bigmodel-coding` share `zai.svg`: Z.AI and BigModel
+are the same company, and the mainland console publishes only the wordmark.