fix: show sidebar reads in profile reads tab when main articles array is empty

[mstrofnone]

Problem

When visiting a profile that has published reads (long-form notes), the profile stats correctly show e.g. "2 reads", but clicking the Reads tab displays "${name} hasn't published any reads".

Reproduce: Visit https://primal.net/p/nprofile1qqsyxxz7mm9kwkyjsf935da90ulyqlaautk6wgq68q5m3n6t5lzmfuqur0zgt — the profile shows 2 reads, but clicking the Reads tab shows "mstrofnone hasn't published any reads".

Root Cause

The profile page makes two separate fetches for reads:

1. Sidebar fetch (ProfileContext, ~line 906): fetches up to 2 articles via fetchMegaFeed and stores them in sidebarArticles.notes
2. Tab fetch (ProfileTabs, ~line 172): fetches articles via getProfileMegaFeed when the Reads tab is clicked, storing them in articles

The Reads tab in ProfileTabs.tsx only checks profile.articles.length to determine whether to show the empty state message. When the main articles array is empty (either because the tab hasn't been clicked yet, or the mega feed request returned empty), it shows the "hasn't published any reads" message — even though sidebarArticles.notes has the user's reads.

Fix

Check sidebarArticles.notes as a fallback in three places within the Reads tab:

1. Skeleton loader: only show loading skeletons when both articles and sidebarArticles.notes are empty
2. Empty state message: only show "hasn't published any reads" when both arrays are empty
3. Article list: show articles from sidebarArticles.notes when articles is empty but sidebar data exists

This is a minimal, targeted fix (4 lines changed) that doesn't alter data fetching logic or other tabs.