Play Framework

docs: fix out-of-sequence javadoc headings in ExtendedConnectWebSocketHandler

Javadoc renders the class name as <h1>, so the first heading in a class comment
must be <h2>. The three section headings here started at <h3>, which skips a
level - a real screen-reader defect (WCAG 1.3.1), and doclint's accessibility
group failed the build with "heading used out of sequence".

Every `ant javadoc` since PF-157 has reported "1 error" because of this. Only
one surfaced despite three offending headings: doclint reports the first
out-of-sequence heading, then treats later siblings at the same level as in
sequence. <h2> also matches the convention already used in LegacyCache.

Comment-only change; `ant test` passes and `ant javadoc` is now error-free.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>