fix: parse closing tags without matching opening tags (#149)

[maruthang]

Summary

Fixes #149

Bug: The HTML parser silently discarded closing tags that had no matching opening tag (e.g., </div> appearing without a prior <div>), making it impossible for consumers to detect orphan closing tags.

Root Cause: In htmlParser.ts, the EndTagClose branch only handled the case where a matching ancestor was found. When no match existed, the closing tag was simply ignored with no node created.

Fix: Added an else branch that creates an "orphan" node for unmatched closing tags. The node has endTagStart set but no startTagEnd, allowing consumers to detect orphan closing tags by checking node.endTagStart !== undefined && node.startTagEnd === undefined.

Changes

• src/parser/htmlParser.ts: When no matching opening tag is found for a closing tag, create an orphan node with endTagStart set and add it as a child of the current node.
• src/test/parser.test.ts: Updated existing MissingTags test expectations and added new regression tests for standalone closing tags, mismatched closing tags, and multiple orphan closing tags.

Testing

• Added regression tests in src/test/parser.test.ts (Closing tag without opening tag (issue #149)) that verify orphan closing tags are properly represented in the parse tree.
• Updated existing MissingTags test expectations to match the new behavior.
• All 154 tests pass.