UI readability pass and Bazaar in-app purchase bridge

- muted text #9e9ec0 -> #727299 (contrast 2.6 -> 4.5 on white); tab labels 11px
- map: chapter titles wrap to two lines instead of being cut off
- reduced-motion respected (MotionConfig + CSS), focus-visible ring,
  no pull-to-refresh, short vibration on correct/wrong answers
- src/lib/bazaar.ts: bridge to the Android WebView wrapper; checkout uses
  Bazaar IAP only inside that app, Zarinpal everywhere else (unchanged)
- android/: WebView wrapper with Poolakey; written but never built

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/build.gradle.kts

@@ -0,0 +1,4 @@
+plugins {
+    id("com.android.application") version "8.5.2" apply false
+    id("org.jetbrains.kotlin.android") version "1.9.24" apply false
+}