v26.9.4

Plugin package version 26.9.4, with the mariadb-shell MCP server floor
(MARIADB_SHELL_VERSION) pinned to 26.9.4 across all ten plugins. The two
versions are set by different scripts and are independent of each other;
they happen to coincide at this release. mariadb-shell 26.9.4 was
already released when the floor moved.

No skill changed in this release. The skills were re-vendored from
mariadb-docs at bb6522c and from mariadb-shell at 8adaada, but nothing
under either source's skill tree had moved, so only the provenance in
each plugin's skills-source.json changed. Counts hold at 82 skills for
the dev plugins, 47 for sql and 2 for contributor.

Also in this release: a /release command for maintainers, which runs
this whole flow from the mariadb-shell version check to the fork sync
(repo tooling only, not shipped inside any plugin).

See each plugin's CHANGELOG.md [26.9.4] section for details.