feat(providers): add four OpenAI-compatible aggregator providers (dahl, atria, agnes, bai)

Adds Dahl Inference, Atria Dawn, Agnes AI, and B.AI following the existing
registry pattern. Each uses DefaultExecutor with no custom translator needed.

open-sse/providers/registry/atria.js

@@ -0,0 +1,32 @@
+export default {
+  id: "atria",
+  priority: 120,
+  alias: "atria",
+  aliases: [
+    "atria-asi",
+  ],
+  uiAlias: "atria",
+  display: {
+    name: "Atria Dawn",
+    icon: "flare",
+    color: "#C2410C",
+    textIcon: "AD",
+    website: "https://atria-asi.ai",
+    notice: {
+      text: "OpenAI-compatible endpoint from Atria Dawn (AtomInnoLab). Currently a research preview offering a single text model, Atria-Dawn-Preview.",
+      apiKeyUrl: "https://api.atria-asi.ai/dashboard",
+    },
+  },
+  category: "apikey",
+  authType: "apikey",
+  transport: {
+    baseUrl: "https://api.atria-asi.ai/v1/chat/completions",
+    validateUrl: "https://api.atria-asi.ai/v1/models",
+  },
+  // Docs pin the model field to one case-sensitive id. Text-only for now: the
+  // service ships a hook that blocks image/PDF input, so no vision is claimed.
+  models: [
+    { id: "Atria-Dawn-Preview", name: "Atria Dawn Preview" },
+  ],
+  passthroughModels: true,
+};