feat(providers): add Poolside provider (OpenAI-compatible)

Adds Poolside (inference.poolside.ai) as an API-key provider using the default OpenAI transport. Registers three Laguna models with reasoning capabilities (262K context, 32K max output).

open-sse/providers/registry/poolside.js

@@ -0,0 +1,31 @@
+export default {
+  id: "poolside",
+  priority: 60,
+  alias: "poolside",
+  aliases: [
+    "ps",
+  ],
+  uiAlias: "ps",
+  display: {
+    name: "Poolside",
+    icon: "water_drop",
+    color: "#0EA5E9",
+    textIcon: "PS",
+    website: "https://poolside.ai",
+    notice: {
+      apiKeyUrl: "https://platform.poolside.ai/api-keys",
+    },
+  },
+  category: "freeTier",
+  authType: "apikey",
+  authModes: ["apikey"],
+  transport: {
+    baseUrl: "https://inference.poolside.ai/v1/chat/completions",
+    validateUrl: "https://inference.poolside.ai/v1/models",
+  },
+  models: [
+    { id: "poolside/laguna-s-2.1", name: "Laguna S 2.1" },
+    { id: "poolside/laguna-xs-2.1", name: "Laguna XS 2.1" },
+    { id: "poolside/laguna-m.1", name: "Laguna M.1" },
+  ],
+};