Play Framework

chore(deps)!: remove GPL mysql-connector-j and drop jj-simplecaptcha/Images.captcha (PF-148)

A downstream license audit flagged the only two non-permissive jars bundled in
framework/lib; because framework/lib is copied verbatim into every downstream
`play bundle`, both propagated into every shipped binary.

- Remove mysql-connector-j 9.3.0 (GPL-2.0 w/ FOSS Exception). It was a pure
  optional runtime JDBC driver -- no `import com.mysql` in framework/src -- so
  no framework feature is lost; MySQL apps supply their own driver. This deletes
  the entire "GPL-2.0 with FOSS Exception" NOTICE section, making every
  downstream bundle GPL-free.
- Drop jj-simplecaptcha and the play.libs.Images.captcha() / Images.Captcha API
  it backed (loosely-stated license). Prune the VENDORED_JARS entry, the NOTICE
  attribution, and rework the guide5 captcha tutorial (EN + JA) to point at an
  external captcha service while keeping the stateless-Cache validation lesson.

Adds a configuration.textile note that MySQL users bring their own connector.
ant test (clean -> jar -> unittest -> integration-test) green.

BREAKING CHANGE: play.libs.Images.captcha() and Images.Captcha are removed.
Apps using the bundled captcha generator must integrate an external captcha
service (reCAPTCHA, hCaptcha, Cloudflare Turnstile). MySQL apps must add a JDBC
driver dependency (com.mysql:mysql-connector-j or org.mariadb.jdbc:mariadb-java-client).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>