refactor: extract provider logic into modular registry

Each AI provider now has its own module implementing a ProviderModule
interface with createGateway, getAuthHeaders, and fetchModels methods.
This replaces the monolithic switch statements in ai-provider.ts and
models.post.ts with a clean registry pattern.

server/utils/providers/closedrouter.ts

@@ -0,0 +1,63 @@
+import { createOpenAI } from '@ai-sdk/openai';
+import { GatewayFetchError } from '~~/server/utils/ai-provider';
+import { Err, Ok } from '~~/types/result';
+import type { ProviderModule } from '.';
+
+export default {
+    id: 'closedrouter',
+    baseUrl: 'https://router.queef.in/v1',
+    modelsEndpoint: '/models',
+
+    createGateway({ apiKey, baseURL }) {
+        if (apiKey === undefined) {
+            return Err(GatewayFetchError.NoProviderApiKey);
+        }
+
+        return Ok({
+            gateway: createOpenAI({ name: 'ClosedRouter', apiKey, baseURL }),
+            streamTransformer: undefined,
+            textTransformer: undefined,
+        });
+    },
+
+    getAuthHeaders(apiKey) {
+        return apiKey ? { Authorization: `Bearer ${apiKey}` } : {};
+    },
+
+    async fetchModels({ baseURL, apiKey }) {
+        const res = await fetch(`${baseURL}/models`, {
+            method: 'GET',
+            headers: { Authorization: `Bearer ${apiKey}` },
+        });
+        const data = await res.json();
+
+        if (!res.ok) {
+            throw createError({ statusCode: res.status, message: JSON.stringify(data) });
+        }
+
+        return data.data.map((model: any) => {
+            const capabilities = new Array<string>();
+
+            if (model.capabilities) {
+                if (model.capabilities.reasoning) {
+                    capabilities.push('reasoning');
+                }
+                if (model.capabilities.tool_call) {
+                    capabilities.push('tools');
+                }
+            }
+
+            return {
+                id: model.id,
+                name: model.name,
+                attributes: {
+                    inputModalities: model.modalities?.input || ['text'],
+                    outputModalities: model.modalities?.output || ['text'],
+                    capabilities: capabilities,
+                    contextWindow: model.context_window,
+                    supported_parameters: [],
+                },
+            };
+        });
+    },
+} satisfies ProviderModule;