feat(player): Alt/Ctrl + scroll to change playback speed

[mohamedashraf011]

Summary

This PR adds an optional hotkey to change YouTube playback speed using the mouse wheel:

• Default behavior: Hold Alt and scroll to adjust speed by ±0.1.
• Optional toggle: Users can switch to Ctrl + scroll via a setting.

Rationale: Ctrl + scroll is handled by the browser as page zoom and cannot be reliably prevented from a content script. Therefore, Alt + scroll is enabled by default, with an opt-in to Ctrl for users who prefer it or have page zoom disabled.

UX

• While the modifier key is held, scrolling increases/decreases playbackRate in 0.1 steps.
• Speed is clamped (e.g., 0.1–16).
• A small overlay appears on the player (e.g., “1.2×”) and fades after ~1s.
• Works on watch pages and Shorts (same player hook); excluded on /tv and audiolibrary like other features.

Settings (Player → Playback)

• “Change speed with Alt + Scroll” [On/Off] (default: On)
• “Use Ctrl instead of Alt (may conflict with browser zoom)” [On/Off] (default: Off)

Technical notes

• Listens to wheel events on the player/video element.
• Uses the modifier guard: e.altKey || (useCtrl && e.ctrlKey).
• For trackpads/low deltas, change is applied per directional step (with a small threshold) to avoid over-sensitivity.
• No preventDefault() on Ctrl + scroll (browser zoom takes precedence by design).
• Keeps integration with existing playback speed state; clamping ensures no out-of-range values.

i18n

Added minimal English strings (other locales fall back to en):

• alt_scroll_speed_name: "Change speed with Alt + Scroll"
• alt_scroll_speed_desc: "Hold Alt and use the mouse wheel to change playback speed."
• use_ctrl_instead_of_alt_name: "Use Ctrl instead of Alt (may conflict with browser zoom)"
• use_ctrl_instead_of_alt_desc: "Hold Ctrl and scroll to change playback speed. Note: browsers use Ctrl + scroll for page zoom."

Testing

• ✅ Chrome 139 / Windows: watch page, theatre, fullscreen
• ✅ Shorts player
• ✅ Page zoom unaffected with Alt; browser zoom remains active with Ctrl (as expected)
• ✅ Overlay renders and disappears correctly; no layout shift
• ✅ No new permissions; manifest unchanged (content script only)

Limitations

• Ctrl + scroll continues to trigger browser zoom; this is expected and documented. Alt is the safe default.
• On some trackpads, very small deltas are coalesced; we step by direction to keep UX predictable.

Screenshots/GIF (optional)

If needed I can add a short GIF demo of Alt + scroll on a watch page.

Checklist

• Follows project contributing guidelines (feature + i18n strings)
• English locale keys added
• No permissions or manifest changes required for default path
• Manually tested on watch/Shorts
• Linked issue

Closes #3105

[ImprovedTube]

hi and thanks! @mohamedashraf011

a toggle is missing in the extension popup menu. (most of all) our code only runs, when a toggle is enabling a feature.

(an english message wasnt added for that either. instead the Chinese messages were reformatted.

Can you share the methodology? /Which AI, parameters and prompt were used for what step?)