ci(release): replace Python heredoc with printf for signing config injection

The Python heredoc had TOML section lines at column 0 inside a YAML
literal block, which YAML interprets as terminating the block (parse
error, instant workflow failure). printf keeps all lines at proper
indentation within the run block while avoiding sed escaping issues
with special characters in passwords.

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

.github/workflows/release.yml

@@ -107,8 +107,9 @@ jobs:
 
       - name: Inject release signing config
         # cargo-apk --release requires [package.metadata.android.signing.release]
-        # in solitaire_app/Cargo.toml. We append it at CI time so secrets never
-        # live in the repo. Python avoids sed escaping issues with special chars.
+        # in solitaire_app/Cargo.toml. Appended at CI time so secrets never
+        # live in the repo. printf keeps every line inside the YAML run block,
+        # avoiding the YAML parse error a heredoc with column-0 content causes.
         env:
           ANDROID_KEYSTORE_BASE64: ${{ secrets.ANDROID_KEYSTORE_BASE64 }}
           ANDROID_KEYSTORE_PASSWORD: ${{ secrets.ANDROID_KEYSTORE_PASSWORD }}
@@ -116,20 +117,13 @@ jobs:
           ANDROID_KEY_PASSWORD: ${{ secrets.ANDROID_KEY_PASSWORD }}
         run: |
           echo "$ANDROID_KEYSTORE_BASE64" | base64 -d > release.keystore
-          python3 - << 'PYEOF'
-          import os
-          workspace = os.environ['GITHUB_WORKSPACE']
-          ks_path = f"{workspace}/release.keystore"
-          section = f"""
-[package.metadata.android.signing.release]
-path = "{ks_path}"
-keystore_password = "{os.environ['ANDROID_KEYSTORE_PASSWORD']}"
-key_alias = "{os.environ['ANDROID_KEY_ALIAS']}"
-key_password = "{os.environ['ANDROID_KEY_PASSWORD']}"
-"""
-          with open('solitaire_app/Cargo.toml', 'a') as f:
-              f.write(section)
-          PYEOF
+          {
+            printf '\n[package.metadata.android.signing.release]\n'
+            printf 'path = "%s"\n'             "${GITHUB_WORKSPACE}/release.keystore"
+            printf 'keystore_password = "%s"\n' "$ANDROID_KEYSTORE_PASSWORD"
+            printf 'key_alias = "%s"\n'        "$ANDROID_KEY_ALIAS"
+            printf 'key_password = "%s"\n'     "$ANDROID_KEY_PASSWORD"
+          } >> solitaire_app/Cargo.toml
 
       - name: Build and sign APK (release profile)
         run: cargo apk build -p solitaire_app --release