fix: code-in-table CSS sizing + markdown image rendering (#486, #487)

- static/style.css: add td code / th code rules (font-size 0.85em,
  padding 1px 4px, vertical-align baseline) for both .msg-body and
  .preview-md to fix cramped inline code in table cells (#486)

- static/ui.js inlineMd(): add image pass (![alt](url) → <img
  class=msg-media-img>) running while _code_stash is active (protects
  image syntax inside backticks), add _img_stash (\x00G) to shield
  rendered <img> src= from autolink, add img to SAFE_INLINE (#487)

- static/ui.js renderMd() outer: add image pass before outer link pass
  for images in plain paragraphs, add img to SAFE_TAGS allowlist (#487)

- tests/test_issue486_487.py: 45 new tests covering CSS source checks,
  JS source structure, rendering behaviour, and combination edge cases
  (code + image + link in same table cell, image inside code span, etc.)

Closes #486, closes #487

static/index.html

@@ -536,7 +536,7 @@
                 <div class="settings-section-title">System</div>
                 <div class="settings-section-meta">Instance version and access controls.</div>
               </div>
-              <span class="settings-version-badge">v0.50.43</span>
+              <span class="settings-version-badge">v0.50.44</span>
             </div>
             <div class="settings-field" style="border-top:1px solid var(--border);padding-top:12px;margin-top:8px">
               <label for="settingsPassword" data-i18n="settings_label_password">Access Password</label>