chore: gitignore keystores and refresh Cargo.lock

Adds *.jks / *.jks.bak / *.keystore to .gitignore so the
release signing material can never be committed accidentally.

Cargo.lock drift catches up with 7c07f71 (bevy dep added to
solitaire_data for Android target) — the prior commit edited
solitaire_data/Cargo.toml but didn't regenerate the lockfile.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -10,3 +10,8 @@ data/
 
 # IDE project files
 .idea/
+
+# Android signing keystores — never commit
+*.jks
+*.jks.bak
+*.keystore