catalogue: add io.pilot.mysql 9.7.1 (native MySQL server+client)

[Alexgodoroja]

Add io.pilot.mysql 9.7.1 to the app-store catalogue

Companion to app-template pilot-protocol/app-template#74 (merged). Adds MySQL 9.7.1 — the full server (mysqld) + client suite as a native app: a real, local client/server RDBMS with no cloud account and no provisioning. The transactional, server-grade sibling of io.pilot.sqlite (embedded) and io.pilot.postgres.

Entry

• Signed catalogue.json entry + catalogue/apps/io.pilot.mysql/metadata.json (sha-pinned).
• All artifacts on prod R2: four platform adapter bundles at bundles/io.pilot.mysql/9.7.1/ (darwin+linux × arm64+amd64), each bundle_sha256-pinned; their install.json stages the MySQL binaries from io.pilot.mysql/9.7.1/… on prod R2 (no dev dependency at runtime).
• Publisher: ed25519:cTZr4unmAHK/r8fS+TVQ4QiCIORimYe+y+bIdiUUfAY=; catalogue.json.sig re-signed with the production key, verifies against the catalogtrust anchor.

Methods (13 + auto help): initialize, start, stop, ping, createdb, query (aligned table), query_tsv, databases, tables, dump (mysqldump), exec (verbatim argv + stdin), mysql_help, version.

Verified: pilot-app verify on all four bundles; macOS socket-mode + a fresh Linux (aarch64) microVM install from a local catalogue exercise the whole lifecycle against the real prod-R2-staged server — initialize → start → createdb → CREATE TABLE + INSERT + SELECT (aligned + TSV) → SHOW TABLES → mysqldump → stop.

Go-live change (installs for all agents). A mysqlctl dispatcher wires basedir/plugin-dir/error-messages to the staged path so the relocated server runs; MySQL must not run as OS root, which suits the unprivileged Pilot daemon.

[Alexgodoroja]

Superseded by #360, which bundles this change with the other three open catalogue PRs so the shared catalogue.json/catalogue.json.sig is signed and reviewed once instead of each merge invalidating the others. This PR's entry and files were taken verbatim into #360. Closing; not deleting the branch in case we need to reopen.