Autoplay switch: always in the bar, like YouTube's

[Nawid3333]

The problem (your report, 2026-10-11)

The autoplay switch from #431 sat in one tool together with the Next button. The player hides that tool whenever FastStream finds no next-episode link on the page (hasNextVideo()), so on most pages the switch was simply never there. Turning the setting on in the options page didn't change that.

Now

• The switch is a tool of its own (autoplay): on the left, right after Next, and movable like every other tool. Saved toolbars get it merged in automatically.
• Next shows only when there is a next episode; the switch always shows.
• Look: like YouTube's. The knob shows ▶ when autoplay is on and ❚❚ when it's off; the track turns teal when on. It uses the theme's colours.
• Behaviour is unchanged: the switch sets autoplay for this tab; the options-page setting is the default for new tabs.

Off	On
grey track, knob left with ❚❚	teal track, knob right with ▶, the "Auto" badge on Next

Tests

• player-controls e2e: the switch is visible and works with no next link; Next is hidden then; with a next link, both are shown; also keyboard (Space).
  • Locally 22/22.
  • With the old hiding put back: 21 passing, 1 failing.
• Lint, typecheck, vitest 2260.
• A screenshot of the bar, taken in the test Firefox, confirms the look.

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