refactor: minor nakamoto improvements

[hugocaillard]

Description

• Update blocks color in devnet UI, differentiate new nakamoto blocks vs regular "coinbase" blocks
• Update default stacks-node image

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (e21ae6e) 41.79% compared to head (a8c0991) 41.81%.

Files	Patch %	Lines
components/stacks-network/src/ui/app.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1327      +/-   ##
===========================================
+ Coverage    41.79%   41.81%   +0.01%     
===========================================
  Files           87       87              
  Lines        32028    32028              
===========================================
+ Hits         13387    13391       +4     
+ Misses       18641    18637       -4     

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