feat(android): pure-Kotlin foundation — AW0 scaffold + AW1 modules (218 tests green)

Implements the verifiable pure-Kotlin core of the Android client per
docs/ANDROID_CLIENT_PLAN.md, mirroring the iOS SPM package set as Gradle modules.
Built + reviewed via multi-agent workflow (explore→implement→verify→review),
then review findings fixed with regression tests.

Modules (all pure JVM, kotlin("jvm"); Android-framework modules scaffolded but
gated off in settings — no Android SDK in this env):
- :wire-protocol  — frozen wire contract (sealed Client/ServerMessage, enums,
  HostEndpoint CSWSH origin derivation, transport interfaces), hand-rolled codec
  byte-identical to the server's JSON.stringify + tolerant kotlinx decode.
- :session-core   — ReconnectMachine (1→2→4→8→16→30 backoff), PingScheduler,
  GateTracker (two-line epoch guard), AwayDigest, UnreadLedger, TitleSanitizer,
  KeyByteMap (byte-matches public/keybar.ts).
- :api-client     — all REST routes, tolerant decode, Origin-iff-guarded, prefs
  unknown-key preservation, pairing probe + host-tier classifier.
- :client-tls     — pure half: PKCS#12 parse, X509KeyManager alias logic,
  CertificateSummary, provider-agnostic wrong-passphrase classification.
- :test-support   — FakeTransport / FakeHttpTransport / virtual-clock fakes.

Verify: ./gradlew clean test → 218 tests, 0 failures (wire-protocol 47,
session-core 60, api-client 69, client-tls 27, test-support 15).

Review (3 lenses, 8/10 each) findings fixed: sessionId JSON-injection escape,
CancellationException propagation in PingScheduler, PairingProbe close-on-cancel
leak, HostEndpoint trim, HostClassifier hoisted to :wire-protocol (type unified),
BouncyCastle-portable wrong-passphrase detection, lone-surrogate escaping.

Known gap (documented, deferred): /push/fcm-token has no server route yet —
plan task A33 (src/push/fcm.ts) delivers it.

android/session-core/build.gradle.kts

@@ -0,0 +1,28 @@
+// :session-core — pure reducers/state machines (SessionEngine, ReconnectMachine,
+// PingScheduler, GateTracker, AwayDigest, UnreadLedger, KeyByteMap, TitleSanitizer,
+// SessionEvent). Consumes TermTransport by interface only; runs entirely under
+// runTest virtual time. Depends only on :wire-protocol.
+
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+    alias(libs.plugins.kotlin.serialization)
+}
+
+kotlin {
+    jvmToolchain(17)
+}
+
+dependencies {
+    api(project(":wire-protocol"))
+    implementation(libs.kotlinx.coroutines.core)
+
+    // Fakes (FakeConnectionPinger, ...) + TestScope/virtual-time, exposed as `api` by
+    // :test-support, so reducers can be driven under runTest without inventing a clock seam.
+    testImplementation(project(":test-support"))
+    testImplementation(libs.bundles.unit.test)
+    testRuntimeOnly(libs.junit.platform.launcher)
+}
+
+tasks.test {
+    useJUnitPlatform()
+}