feat(voice): SSE bridge + Siri-blob overlay for wake-word script

Adds the tablet side of voice assistant integration. External Python
script (openWakeWord + Groq STT + OpenClaw) will POST state transitions
to /api/voice/event with a bearer token, and the tablet shows a
fullscreen overlay with Siri-style animated blob + current agent +
recognized text / response text.

- lib/voice-bus.ts — in-process EventEmitter singleton, preserved
  across hot reloads via globalThis
- app/api/voice/event — POST, bearer-auth via VOICE_API_KEY env,
  validates event kind, broadcasts on voiceBus
- app/api/voice/stream — GET, SSE endpoint, per-connection listener
  with 15s keep-alive ping and abort-signal cleanup
- components/VoiceOverlay — full-screen overlay, 3-layer pulsing
  Siri blob, per-agent palette (cosmo indigo/violet, lusya pink/rose),
  auto-dismiss timeouts (wake=20s safety, response=6s, error=4s),
  auto-reconnect on SSE drop
- middleware bypasses /api/voice/event so the script does not need
  a user auth cookie
- VoiceOverlay mounted in HomePageInner outside tab routing so it
  appears on every view

app/api/voice/event/route.ts

@@ -0,0 +1,37 @@
+export const dynamic = 'force-dynamic'
+export const runtime = 'nodejs'
+
+import { NextResponse } from 'next/server'
+import { voiceBus, VoiceEventPayload } from '@/lib/voice-bus'
+
+const ALLOWED_EVENTS = new Set(['wake', 'command', 'response', 'idle', 'error'])
+
+export async function POST(req: Request) {
+  const expected = process.env.VOICE_API_KEY
+  if (!expected) {
+    return NextResponse.json({ error: 'voice_not_configured' }, { status: 503 })
+  }
+
+  const auth = req.headers.get('authorization') || ''
+  const token = auth.replace(/^Bearer\s+/i, '').trim()
+  if (token !== expected) {
+    return NextResponse.json({ error: 'unauthorized' }, { status: 401 })
+  }
+
+  const body = await req.json().catch(() => null)
+  if (!body || typeof body.event !== 'string' || !ALLOWED_EVENTS.has(body.event)) {
+    return NextResponse.json({ error: 'invalid_event' }, { status: 400 })
+  }
+
+  const agent = body.agent === 'lusya' ? 'lusya' : body.agent === 'cosmo' ? 'cosmo' : undefined
+
+  const evt: VoiceEventPayload = {
+    event: body.event,
+    agent,
+    text: typeof body.text === 'string' ? body.text.slice(0, 2000) : undefined,
+    timestamp: new Date().toISOString(),
+  }
+
+  voiceBus.emit('voice', evt)
+  return NextResponse.json({ ok: true })
+}