Anchor the #endregion folding marker

[Ngo Quoc Viet (NgoQuocViet2001)]

Problem

htmlFolding.ts detects region markers with:

const m = text.match(/^\s*#(region\b)|(endregion\b)/);

Alternation binds looser than the anchor, so this reads as (^\s*#region\b) or (endregion\b) — the second branch is unanchored and matches the word anywhere in a comment.

Effect

Measured with getFoldingRanges on the built library:

input	ranges
#region … a harmless multi-line comment … #endregion	{3-5 comment}, {0-7 region} ✓
the same, with the comment containing the word endregion	{0-3 region} ✗
a standalone multi-line comment	{0-4 comment} ✓
the same comment containing the word endregion	[] ✗

Two things go wrong at once. The open #region is closed at the prose comment instead of at its real marker, so the fold covers the wrong span; and because that comment was consumed as a marker, it also loses its own folding range.

An HTML comment that documents region markers — or any prose that happens to contain the word — is enough to trigger it.

Fix

Group the alternation so the anchor covers both branches:

const m = text.match(/^\s*#(?:(region\b)|(endregion\b))/);

Capture-group numbering is unchanged, so the m[1] / m[2] branches below need no edit.

Test plan

• Added two cases to src/test/folding.test.ts beside the existing Fold regions: a region whose body contains a comment mentioning endregion, and a standalone comment containing the word.
• Ran: node --test ./lib/esm/test/*.test.js → 178 passing (176 before).
• Checked: reverting only htmlFolding.ts fails both new tests.
• Ran: npm run lint → clean.