Enhancement: Add a pop-up promoting the "Meu Candidato" Catarse campaign

### Background Information

We launched "Meu Candidato" as a crowdfunding campaign on Catarse
(catarse.com.br/meucandidato), with a deadline in October 2026. Right now
the platform has no touchpoint with that campaign — anyone visiting
aletheiafact.org has no way of knowing it exists unless they already follow
our social media. We need a way to expose the campaign to people who are
already on the site, instead of relying only on external promotion.

### Steps to Reproduce

1. Visit any page on aletheiafact.org
2. Browse the site normally

**Current result:** there is no mention of the Catarse campaign at any
point during navigation.

### How

Add a pop-up that appears to the user on any page of the site, with a
short delay after load, showing the campaign pitch and a button that
opens `catarse.com.br/meucandidato` in a new tab. Dismissing the pop-up
(the close icon, "Not now", or clicking the support button) should be
remembered so it doesn't keep reappearing on every page load — but since
the campaign has a deadline, it should come back after some days rather
than being hidden forever. It should also be possible to turn the pop-up
on/off without a full deploy (a feature flag/env var), so it can be
switched off once the campaign ends.

### Expected Behavior

- A pop-up shows on first visit to any page, after a brief delay, with
the campaign pitch and a clear CTA linking to
`catarse.com.br/meucandidato` (new tab)
- Closing the pop-up in any way (X, "Not now", or the CTA) hides it for
about a week before it can show again
- The pop-up can be toggled on/off via configuration, without a code
change
- The existing donation banner is turned off while this campaign is
running, so users aren't shown two competing funding asks at once

The issue names no files or tests. Start by locating the shared entry point used by pages on aletheiafact.org and the existing donation banner implementation, then trace how configuration or environment flags and client-side dismissal state are handled. Done means the campaign pop-up appears and can be dismissed, reappears after about a week, respects the toggle, and does not compete with the donation banner.

索引モデルが issue の本文から書いたものです。