Banner flashes briefly on page reload when previously dismissed

[RisingOrange]

Description

When a user dismisses a banner and then reloads the page, the banner briefly flashes visible before hiding itself. This affects both regular banners and campaign banners.

2026-02-21.20-53-24.mp4

Root cause

The dismissed state is stored in localStorage, but reading it happens too late:

1. Server renders HTML with banner visible (no localStorage access on server)
2. Browser receives HTML and paints it → banner is visible
3. JS bundle loads and Svelte hydrates
4. onMount fires → reads localStorage → hides banner

The flash occurs in steps 2–3, before any JS runs.

Steps to reproduce

1. Visit the site
2. Dismiss a banner
3. Reload the page
4. Observe the banner flashing briefly before disappearing

Fix

PR #663