feat: LLM provider switcher (Claude/Groq) in settings tab

app/api/settings/route.ts

@@ -0,0 +1,33 @@
+export const dynamic = 'force-dynamic'
+import { NextRequest, NextResponse } from 'next/server'
+import { promises as fs } from 'node:fs'
+import path from 'node:path'
+
+const SETTINGS_PATH = '/data/settings.json'
+const DEFAULTS = {
+  voiceProvider: 'anthropic',
+  anthropicModel: 'claude-haiku-4-5-20251001',
+  groqModel: 'llama-3.3-70b-versatile',
+}
+
+async function readSettings() {
+  try {
+    const raw = await fs.readFile(SETTINGS_PATH, 'utf-8')
+    return { ...DEFAULTS, ...JSON.parse(raw) }
+  } catch {
+    return { ...DEFAULTS }
+  }
+}
+
+export async function GET() {
+  return NextResponse.json(await readSettings())
+}
+
+export async function POST(req: NextRequest) {
+  const body = await req.json()
+  const current = await readSettings()
+  const updated = { ...current, ...body }
+  await fs.mkdir(path.dirname(SETTINGS_PATH), { recursive: true })
+  await fs.writeFile(SETTINGS_PATH, JSON.stringify(updated, null, 2), 'utf-8')
+  return NextResponse.json(updated)
+}