fix(render): prevent trade-friendly ships from visually rendering as angry red warships (#3843) (#4017)

## Description: 

The unit fragment shader (unit.frag.glsl) checked vFlags > 1.5 to
colorize warships in their attacking/angry solid red territory band
(FLAG_ANGRY = 2.0). However, trade-friendly ships use
FLAG_TRADE_FRIENDLY = 3.0 which also matched this condition, causing
friendly/trade-allied ships to incorrectly render as hostile/angry
warships in normal camera view.

This fix refactors unit.frag.glsl to use precise float range queries via
abs() to verify FLAG_ANGRY and FLAG_FLICKER flags specifically,
preventing the trade-friendly flag from triggering the angry-red
colorization.

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [X] I have added relevant tests to the test directory
- [X] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

barfires