feat: make taxation unit indicators closer to gov.br inputs (#84)

* feat(settings-view): use gov.br-like in-field unit affordances in taxation tab

Replace the standalone unit legend with subtle in-field suffix affordances
for monetary and percentage fields, similar to the visual cue pattern used
by gov.br inputs.

Signed-off-by: Vitor Mattos <vitor@php.rio>

* test(view): cover gov.br-like taxation unit affordances

Signed-off-by: Vitor Mattos <vitor@php.rio>

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Signed-off-by: Vitor Mattos <vitor@php.rio>

Author: vitormattos