CB-602: guard against a config key that never reaches the example

BridgedConfig.KNOWN_TOP_LEVEL_KEYS is now package-private so a test can assert
every key the parser accepts appears in bridged.example.yaml — live or
commented-out, since the file is gitignored and the example is the only
committed description of the config schema. The existing tests only checked
the example->code direction; this adds code->example.

bridged/src/main/java/dev/ltms/bridged/config/BridgedConfig.java

@@ -967,8 +967,12 @@ public record BridgedConfig(
     /**
      * Top-level keys this version understands. Used only to warn about the rest — see
      * {@link #warnUnknownTopLevelKeys}. Keep in step with the record components.
+     *
+     * <p>Package-private (not {@code private}) so a test can assert every key here is documented in
+     * {@code bridged.example.yaml} — the only committed description of the config schema, since
+     * {@code bridged.yaml} itself is gitignored.
      */
-    private static final Set<String> KNOWN_TOP_LEVEL_KEYS = Set.of(
+    static final Set<String> KNOWN_TOP_LEVEL_KEYS = Set.of(
             "bind", "herdrSocket", "profiles", "guard", "worktreeRoot",
             "lifecycle", "spawnReadyTimeoutMs", "spawnReadyPollMs", "broker", "primary", "fleet",
             "leadHeartbeat", "health", "placement", "auth", "configReload", "quarantineCooldownSeconds");