feat: mock Homarr Assistant in demo mode and fix board page crash

- demo mode now enables the assistant at runtime: getAvailability and
  getRuntimeOptions report an enabled Homarr Assistant (Demo) model without
  requiring a provider configuration or API key
- the assistant chat route returns a canned, streamed answer in demo mode
  instead of calling a real language model
- align the provider/endpoint fields in the assistant configuration page
- catch NOT_FOUND/BAD_REQUEST in the board page so a missing home board
  renders a 404 instead of crashing
- use the camelCase provider options key expected by @ai-sdk/openai-compatible
  to silence the deprecation warning

packages/api/src/router/assistant.ts

@@ -30,7 +30,7 @@ import {
 import type { createTRPCContext } from "../trpc";
 import { fetchOpenRouterGenerationTelemetryAsync } from "../assistant-generation-telemetry";
 import { verifyAssistantGenerationAccessToken } from "../assistant-generation-access";
-import { createTRPCRouter, permissionRequiredProcedure, protectedProcedure } from "../trpc";
+import { createTRPCRouter, isDemoMode, permissionRequiredProcedure, protectedProcedure } from "../trpc";
 import { boardRouter } from "./board";
 
 const adminProcedure = permissionRequiredProcedure.requiresPermission("admin");
@@ -448,6 +448,9 @@ export const assistantRouter = createTRPCRouter({
       },
     })
     .query(async ({ ctx }) => {
+      if (isDemoMode) {
+        return { enabled: true };
+      }
       const configuration = await getConfigurationAsync(ctx.db);
       const requiresApiKey = configuration ? assistantProviderRequiresApiKey(configuration.provider) : false;
       return {
@@ -495,6 +498,24 @@ export const assistantRouter = createTRPCRouter({
 
   getRuntimeOptions: protectedProcedure.query(async ({ ctx }) => {
     const configuration = await getConfigurationAsync(ctx.db);
+    if (isDemoMode) {
+      return {
+        provider: "homarr",
+        defaultModelId: "homarr-assistant",
+        models: [
+          {
+            id: "homarr-assistant",
+            name: "Homarr Assistant (Demo)",
+            description: null,
+            contextLength: null,
+            promptPrice: null,
+            completionPrice: null,
+            inputModalities: [],
+            toolSupport: "unknown" as const,
+          },
+        ],
+      };
+    }
     if (!configuration?.enabled || !configuration.modelId) {
       throw new TRPCError({ code: "PRECONDITION_FAILED", message: "Homarr Assistant is not configured." });
     }