Fix UI-boundary defects; run tests on the Android variant too

Two defects found reviewing the UI boundary before Compose work:

1. HumanAgent.awaiting was a plain mutable property written by the game
   coroutine and read by the UI — a data race, and invisible to Compose. It also
   exposed DecisionContext, which holds a live Seat whose fields mutate as the
   hand proceeds, so even a safe read could observe torn state. Replaced with an
   immutable DecisionOffer published through a StateFlow. A test mutates the live
   seat after publication and asserts the offer does not change.

2. STREET_COMPLETE was emitted after dealing the new street but before the round
   state was reset, so a flop snapshot carried pre-flop currentBet and
   committedThisRound — the UI would have painted last street's chips in front of
   every player alongside the new board. The reset is now prepareRound(), called
   before publishing. Verified: with the ordering reverted the new test fails
   with currentBet 10 on the flop.

Also:
- HumanAgent.cancel() is now covered directly; the previous test only cancelled
  the coroutine running act(). cancel() and submit() both report whether anything
  was actually pending.
- Android host tests enabled via withHostTestBuilder, so the shared suite runs
  against the Android variant instead of the AAR merely compiling.

No librsvg needed for card assets: sips rasterizes the SVGs directly at exact
2:3 dimensions, court cards and patterned backs included.

Tests: 45 -> 48, now green on both jvmTest and testAndroidHostTest.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

engine/build.gradle.kts

@@ -4,7 +4,7 @@ plugins {
 }
 
 kotlin {
-    // JVM target drives tests and the headless tuning simulator.
+    // JVM target drives the headless tuning simulator.
     jvm()
 
     // The modern KMP Android integration. `androidTarget()` is the older path.
@@ -12,6 +12,12 @@ kotlin {
         namespace = "com.jsjdesigns.poker.engine"
         compileSdk = 37
         minSdk = 26
+
+        // Run the shared tests against the Android variant too, not just compile
+        // it — otherwise the AAR is only ever proven to build.
+        withHostTestBuilder {}.configure {
+            isIncludeAndroidResources = true
+        }
     }
 
     sourceSets {