Remove unused code and honor effect rendering flags

[kivutar]

Remove production helpers kept alive only by tests, unused fields and arguments, and redundant window drawing wrappers. Tests now exercise the packet builders, resource loaders, and combat/render helpers used by the game; windows publish through their existing widget path.

Two effect fields represented missing rendering behavior rather than dead code. Sprite effects marked to render before entities now use an earlier pass, and moving effect shadows follow terrain height. Converted effect specifications are cached by ID so the two passes do not rebuild them every frame. The effect ID catalogue is preserved.

Validation: the full CGO_ENABLED=0 go test -tags nofakecgo ./... suite, go vet, and staticcheck pass. New tests cover effect ordering, moving-shadow height, and allocation-free warmed sprite-effect draws. A synthetic 200-tile effect benchmark reduced allocations from 515 KB to 54 KB per frame after caching. Tests requiring an explicitly configured client-data directory retain their existing skips; the effect changes have not yet been checked visually in game.