Pulled from the game's own GameAssets/Assets/Texture2D (gitignored as a
whole, not redistributed wholesale) into a tracked assets/icons/ so
they're actually usable in FeNigma's UI instead of us redrawing
equivalents:
- targets/enemy/, targets/friendly/: one marker per game unit type
('Enemy_*.png' / 'Friendly_*.png', the source files spell the latter
'Frendly_*.png', corrected on copy).
- reference_points/: the four lettered RP markers ('Refrence_Point_*.png'
in the source, typo corrected the same way).
- shells/: one icon per Shell enum member (shells.py), named to match
exactly so they're a direct Shell.name lookup, no mapping table
needed. A few source files don't carry the shell's short code in
their name (Mustard Gas_DemoBlocked -> MSTD, Tear Gas -> TEAR,
Propaganda -> PRPG, Phosgene -> PHGN, Nuclear -> ATMC), documented in
assets/icons/README.md.
- nest/IronNest.png: the Iron Nest/FDC unit icon.
- misc/ScoutPlane.png: fits the scout-flight planning feature.
Also commits the (already-made, previously uncommitted) .gitignore
entry for GameAssets itself, which is what makes pulling individual
icons out into a tracked directory sensible instead of contradictory.
