feat: Add settings API endpoint

- Add GET endpoint to retrieve current settings
- Add POST endpoint to update settings
- Add PUT endpoint to update individual settings fields

app/api/settings/route.ts

@@ -0,0 +1,36 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { settingsManager } from '../../../lib/settings'
+
+export async function GET() {
+  try {
+    const settings = await settingsManager.loadSettings()
+    return NextResponse.json(settings)
+  } catch (e: any) {
+    return NextResponse.json({ error: e.message }, { status: 500 })
+  }
+}
+
+export async function POST(req: NextRequest) {
+  try {
+    const updates = await req.json()
+    const settings = await settingsManager.updateSettings(updates)
+    return NextResponse.json(settings)
+  } catch (e: any) {
+    return NextResponse.json({ error: e.message }, { status: 500 })
+  }
+}
+
+export async function PUT(req: NextRequest) {
+  try {
+    const { symbol, timeframe, layouts } = await req.json()
+    
+    if (symbol) await settingsManager.setSymbol(symbol)
+    if (timeframe) await settingsManager.setTimeframe(timeframe)
+    if (layouts) await settingsManager.setLayouts(layouts)
+    
+    const settings = await settingsManager.loadSettings()
+    return NextResponse.json(settings)
+  } catch (e: any) {
+    return NextResponse.json({ error: e.message }, { status: 500 })
+  }
+}