Editor link detection got smarter, fewer false positives

The editor used to over-eagerly turn text like 5.Store into an auto-linked URL because the default link detection thought the dot-separated format looked URL-ish. Annoying when you're writing ordered lists or referencing version numbers inline.

The link extension now uses a stricter URL pattern and autolink is disabled at type-time. Pasted URLs and explicitly created links still work perfectly; lookalike text no longer gets turned into a broken link.

Same release also tightened the reactive heading selector to detect the actual heading level under the cursor in real time, so it always reflects what you're editing.