ci: validate each example's on-chain overlay too (#85)

The loop parses every compose.yml and stops there, so no
compose.onchain.yml is checked by anything. That is the file nobody runs
before merging, since it needs a wallet, an RPC and a keystore, and the
one most likely to break. Interpolating .env.example also proves that
file still lists every variable the overlay reads.

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

Author: rickstaa

.github/workflows/lint.yml

@@ -32,5 +32,12 @@ jobs:
             example=${dir%/}
             [ -f "$example/compose.yml" ] || continue
             docker compose -f "$example/compose.yml" config --quiet || status=1
+            # The on-chain overlay is the one nobody runs before merging: it needs
+            # a wallet, an RPC and a keystore. Interpolating .env.example also
+            # proves that file still lists every variable the overlay reads.
+            [ -f "$example/compose.onchain.yml" ] || continue
+            docker compose --env-file "$example/.env.example" \
+              -f "$example/compose.yml" -f "$example/compose.onchain.yml" \
+              config --quiet || status=1
           done
           exit $status