v26.9.3

Plugin package version 26.9.3, with the mariadb-shell MCP server floor
(MARIADB_SHELL_VERSION) pinned to 26.9.3 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 26.9.3 was
already released when the floor moved.

No skill changed in this release. The skills were re-vendored from
mariadb-docs at 1a89bd3 and from mariadb-shell at 291bf84, 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: CHANGELOG entries for 26.9.3 and, retroactively,
for 26.9.2 -- which had shipped without any -- so every plugin's
CHANGELOG now runs continuously from 26.9.0. The AI Plugins logos were
re-exported, and the DevHub at https://ai-plugins.mariadb.com/ picked up
an MCP nav link, a mariadb.com-derived primary button and two hero-card
fixes (docs/ only, not shipped inside any plugin).

See each plugin's CHANGELOG.md [26.9.3] section for details.