Adds a new merge commitSha restoration script (`scripts/restore-merge-sha-fn-3878.mjs`) with test coverage to handle a specific FN-3878 merge case, along with a changeset for publishing and a minor plugin vitest config governance alignment across three plugins.
Fusion-Task-Id: FN-3878
Adds a WhatsApp chat plugin (`plugins/fusion-plugin-whatsapp-chat/`) as the first bundled plugin, including the plugin package with UI rendering, dashboard plugin manager integration, CLI bundling support, and plugin route runtime context. Also updates documentation to cover plugin management and ap
Fusion-Task-Id: FN-3714