fix(navscroll): do not auto-scroll to first section on page load

[giulio-leone]

Problem

When a page containing <it-navscroll> loads, it auto-scrolls to the first section anchor. This is jarring and unexpected for users who want to see the top of the page.

Root cause: NavscrollStore.init() programmatically sets the first item as selected, and the #initViewScrollerSubscription() reacts to every selected emission by calling ViewportScroller.scrollToAnchor(). The init emission is indistinguishable from a user-initiated selection.

Solution

Add skip(1) after filter(Boolean) in the scroll subscription pipeline. This ignores the first truthy emission (the programmatic init selection) while preserving scroll behavior for all subsequent user-initiated selections.

// Before
this.#store.selected.pipe(
  filter(Boolean),
  delay(0),
  tap(({ href }) => this.#scroller.scrollToAnchor(href))
).subscribe();

// After
this.#store.selected.pipe(
  filter(Boolean),
  skip(1),  // ignore the programmatic init selection
  delay(0),
  tap(({ href }) => this.#scroller.scrollToAnchor(href))
).subscribe();

Testing

• Added navscroll.component.spec.ts with 5 tests including:
  • ✅ Verifies scrollToAnchor is not called on initial load
  • ✅ Renders all section headings
  • ✅ Displays header text
  • ✅ Renders nav links for each item
• Full test suite: 114/114 SUCCESS

Closes #597

⚠️ This reopens #631 which was accidentally closed due to fork deletion.