fix(validation): keep CP-055's artifact readable in a minified build

The drive of 2026-09-05 exported a validation file whose every key was a
single letter, in the same bundle where the signal capture and the trip
history read fine: ValidationArtifact was added after the keep rules that
cover the other artifacts and was never added to them, so R8 renamed the
fields Gson serialises by reflection.

A validation drive costs a drive. Verified against the unstableRelease
mapping: the class now appears exactly as NavGuidanceProbeArtifact does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: malys

app/proguard-rules.pro

@@ -30,3 +30,9 @@
 -keep class com.evsuite.chargepilot.TripHistoryArtifact { *; }
 -keep class com.evsuite.chargepilot.SpeedScaleCheck$Result { *; }
 -keep class com.evsuite.chargepilot.SpeedScaleCheck$Verdict { *; }
+
+# CP-055's own artifact, added after the rules above and left out of them: the drive of
+# 2026-09-05 exported a validation file whose every key was a single letter, in the same bundle
+# where the capture and the trip history read fine. A validation drive costs a drive.
+-keep class com.evsuite.chargepilot.ValidationArtifact { *; }
+-keep class com.evsuite.chargepilot.ValidationArtifact$Answer { *; }