Add blue variants of the add duplicate buttons

[Kuuuube]

Since we're using green for the add button and red for the add duplicate button it's probably a good idea to have these available in a different color for people who are colorblind. Due to the buttons having a different shape there shouldn't be issues differentiating them but I think it's worth having for potential increased visual clarity for users who may need it.

Unsure about adding a setting for this or how it would be implemented (might be better to make a global colorblind mode?) but by simply adding the svgs we can make it available through custom css and decide later what else to do about this, if anything.

.icon[data-icon="add-duplicate-term-kanji"] { background-image: url('/images/add-duplicate-term-kanji-blue.svg'); }
.icon[data-icon="add-duplicate-term-kana"] { background-image: url('/images/add-duplicate-term-kana-blue.svg'); }

This is how the blue buttons look:

[github-actions]

✔️ No visual differences introduced by this PR.

View Playwright Report (note: open the "playwright-report" artifact)