fix: singing bowls ambient + Next.js 16 async params/cookies

Ambient:
- Replace oscillator drone/melody with singing bowl synthesis
- Each bowl: instant attack + exponential decay (7–12s) = real physical sound
- Two detuned copies per strike for natural shimmer beat
- A-minor pentatonic (A3 C4 D4 E4 G4 A4 C5 E5), weighted toward warm lows
- 30% chance of soft harmonic fifth companion tone per strike
- Random gaps 3–8s between strikes so it breathes naturally
- Two long hall reverb tails (2.4s / 4.8s) for warmth and space
- Graceful 2.5s fade-out on stop

Next.js 16 compatibility (breaking changes from v14→v16):
- Dynamic route params now Promise<{...}> → await params in all handlers
- cookies() now returns Promise → isAdmin() made async, await cookies()
- Files: [...path], memories/[id], media/[id], auth, upload all updated

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/app/api/auth/route.ts

@@ -9,7 +9,7 @@ function getExpectedToken() {
 }
 
 export async function GET() {
-  const cookieStore = cookies()
+  const cookieStore = await cookies()
   const token = cookieStore.get('admin_auth')?.value
   return NextResponse.json({ authed: token === getExpectedToken() })
 }