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