Fix GH-157: Note elements generate semantic HTML using div instead of blockquote

[lacatoire]

Summary

• Replace <blockquote><p> with <div> in format_note(), aligning with format_admonition() used by other admonitions (<caution>, <warning>, <tip>, <important>)
• Change note title from <strong> to <h5 class="title">
• Remove 'note' => 'span' override for simpara, allowing proper <p> rendering inside notes
• Remove 'note' => 'span' override for info, using default format_div
• <sidebar> (which reuses format_note) benefits automatically

Before:

<blockquote class="note"><p><strong class="note">Note</strong>:
  <strong>Custom Title</strong><br />
  <span class="simpara">Content here</span>
</p></blockquote>

After:

<div class="note"><strong class="note">Note</strong>
 <h5 class="title">Custom Title</h5>
 <p class="simpara">Content here</p>
</div>

Test plan

• New test tests/package/generic/note_rendering_001.phpt covering note with and without title
• Full test suite passes (no regressions)

Fixes #157