fix(html): prevent Handlebars tags from corrupting HTML tag stack

[JessenReinhart]

Issue #2045

Handlebars helpers with names matching HTML tags (e.g. {{#tr}}) were incorrectly treated as HTML elements by _do_optional_end_element, which then trashed indentation on the next real HTML tag of the same name.

Root cause

_do_optional_end_element was written for HTML optional-end-element logic but ran on all tags including Handlebars tags. When it encountered {{#tr}}, it matched the HTML tr branch and popped the real <tr> frame off the stack, causing subsequent content inside <td> to be mis-indented.

Fix

Added a 6-line guard at the top of _do_optional_end_element: if the token is a Handlebars tag (tag_start_char === '{'), set parser_token.parent and return immediately — Handlebars tags don't participate in HTML optional-end-element logic.

Changes

• js/src/html/beautifier.js: skip Handlebars tag tokens in _do_optional_end_element.
• test/data/html/tests.js: regression test for {{#tr}} inside a <table>.

Verification

New regression test passes. All 11,960 HTML beautifier tests pass (no regressions).

[bitwiseman]

Nice! Very efficient way to address the immediate issue in a low risk way.