Address the non-test code-review findings on the htmlEmbed sandbox change
(test-coverage gaps are tracked in issue #99):
- html-embed-view: track the iframe's reported content height even while a
fixed height is set, so clearing the height (fixed -> auto) without editing
the source no longer leaves the frame pinned to the stale value. Derive the
fixed-height predicate once; seed autoHeight to the default.
- html-embed-view: drop width/border from the iframe inline style (the
.htmlEmbedFrame CSS class already provides them).
- html-embed-sandbox: coalesce height reports via requestAnimationFrame and
skip <=1px deltas to damp the self-measure feedback loop; fix the misleading
bootstrap comment.
- tracker-settings: add an aria-label to the snippet Textarea (a11y).
- CHANGELOG: note the removal of server-side role-based HTML-embed stripping.
c596e17a40