fix: #3636273 Clicking a same-page anchor link in the Canvas scrolls to its target

Closes #3636273.

The Canvas click handler blocked links but let same-page anchors (#…) through, an exception copied from the Preview in #3562060. In the Canvas a click selects, so following the anchor only scrolled the selected node out of view. Now every a[href] is blocked in the Canvas; the Preview still follows anchors.

Test: builder_frame.spec.ts "A link to an anchor is selected, not followed". It fails without the fix (Canvas scrolls to the target, hash set).

AI-Generated: Yes (fix and test written with Claude, reviewed and run locally by me)