Settings: neutral controls, only Save keeps the accent (#202)

[Maxaubert]

Closes #202.

Owner, 2026-09-23: settings buttons should not follow the accent colour; grey from the background with a slight contrast, the dropdown's colours; only the save buttons stay accented.

• Switch on: track --p-text-soft, knob --p-bg (was the accent).
• Pressed Segmented option: --p-text 16% over --p-control, text --p-text (was the accent).
• Default apps button: the dropdown's look (was accent-tinted).
• Same classes as the terminal core's fields.tsx in Settings: neutral controls, only Save keeps the accent (#42) PrismTerminal#43; the terminal half of this page changes when that core release is bumped in here.
• Kept accented: Save, and the selection marks that are not buttons (style cards, swatches, the rail), Reset links, focus rings.

Version 0.64.0 -> 0.65.0.

Tests: new settingsControls.test.ts (fails on main, 2 of 3); npm test 1579 passed, typecheck, lint 0 errors; e2e =tabs =termOptions =dictationPage =gear all passed.

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