Update Mozilla branding

[janbrasna]

Resolves #765

Logo updated to current lockup, and aligned the same across the og surfaces:

WTN:
http://localhost:8000/en-US/
http://localhost:8000/en-US/survey/
http://localhost:8000/en-US/thunderbird/115.0/beta-appeal/
http://localhost:8000/en-US/thunderbird/128.0/appeal/
http://localhost:8000/en-US/thunderbird/115.0/appeal24/
http://localhost:8000/en-US/thunderbird/115.0/spring24/
http://localhost:8000/en-US/thunderbird/128.0/whatsnew/
UTN:
http://localhost:8000/en-US/
http://localhost:8000/en-US/thunderbird/release/sep25r/
http://localhost:8000/en-US/thunderbird/140.0/whatsnew/
http://localhost:8000/en-US/thunderbird/140.0/jun25a/
http://localhost:8000/en-US/thunderbird/128.0/monthly/
http://localhost:8000/en-US/thunderbird/128.0/apr25/
http://localhost:8000/en-US/thunderbird/128.0/nov24/
http://localhost:8000/en-US/thunderbird/115.0/dec24/

Screenshots [+]

[MelissaAutumn]

Thank you for the PR!

If you have some spare cycles could you left align the mozilla logo at the bottom as mentioned in the issue? (Basically like how https://blog.mozilla.org/en/ has it)

I'll do check out the PR for old appeals later today or early tomorrow (UTC-7).

Thanks again!

[janbrasna]

Now the older footer occurrences are also left-aligned with a new 🏴 logo.

[MelissaAutumn]

I will say @radishmouse has been handling branding updates for stage.tb.pro. Might be good to consolidate any differences from this PR!

[janbrasna]

I'm following the tbpro and common includes, and making this PR deliberately avoiding any overlap — as it's mostly for preexisting content.

I also have a separate change (a few lines) to streamline both wtn+utn with tbpro+common once this merges, it's literally just this d56ff6f +dedupe assets, so the current efforts are well isolated for now, and super easy to blend together once convenient.

[janbrasna]

(Also, re: differences — I too coincidentally had the logo sized to 150px wide originally as tbpro+common now, but later changed to 10rem for consistency with other things in the layout. Maybe that would be a good addition to the tbpro styles later on, if there's more things around it remified? /haven't checked there myself too closely yet/…)