feat(android): replace WebView with tested native Compose API slice

Add real native onboarding/auth/dashboard/tasks/notes/shopping, origin-bound HTTPS and encrypted AndroidKeyStore session persistence. Archive the superseded browser renderer and tests. Verify 10 JVM tests, 6 native API-35 emulator tests, lintDebug/lintRelease and debug/unsigned release APK/AAB builds; the real upstream suite passes 7 tests and exports a nonblank native fixture screenshot. Tink host-tool update removes the old generated-protobuf warning. Full module/visual parity remains explicitly incomplete.

legacy/android/SelectionGate.kt

@@ -0,0 +1,23 @@
+package community.yuvomi.mobile
+
+/** Never delivers a late system-picker result into a different server/web context. */
+class SelectionGate {
+    private var owner: Int? = null
+    val outstanding: Boolean get() = owner != null
+
+    fun begin(generation: Int): Boolean {
+        if (outstanding) return false
+        owner = generation
+        return true
+    }
+
+    fun consume(generation: Int): Boolean {
+        val previous = owner
+        owner = null
+        return previous == generation
+    }
+
+    fun restoreOutstanding() {
+        owner = -1
+    }
+}