Fix macOS subtitle outline toggle and add outline width

[hezhamen]

Summary

macOS subtitle outline On/Off did not change the rendered subs. Custom styling only set sub-outline-size and an ASS Bold= override, so embedded Outline/Shadow stayed. This PR makes outline apply, and adds a width control.

What changed:

• macOS player_bridge.mm: when custom styling is on, also set sub-border-size, sub-border-color, sub-shadow-offset=0, and ASS style overrides Bold=…,Outline=…,Shadow=0. Outline off now sends size 0 and Outline=0.
• Desktop player Style panel: outline toggle still On/Off; width stepper (1–8) and color swatches hide when outline is off.
• Playback settings: outline width slider when outline is enabled.
• Shared settings/model: clamp stored outlineWidth to 1–8; persist was already there, it just had no UI.
• Player controls JSON/JS: send outlineWidth / subtitleOutlineWidthDelta.

PR type

• Reproducible bug fix
• UI glitch/bug fix
• Behavior bug/regression fix
• Small maintenance only, with no UI or behavior change
• Docs accuracy fix
• Translation/localization only
• Approved larger or directional change

Primary fix is the macOS outline toggle not applying. Outline width is a small control on the same setting (outlineWidth already existed in storage).

Why

User-visible bug: Style → Outline On/Off did not add or remove the subtitle border on macOS.

Expected: Off removes the border; On draws it. Width should be adjustable.

Desktop scope

• macOS: native mpv apply path (player_bridge.mm) — this is the actual fix.
• Desktop shared: player overlay HTML/CSS/JS and NativePlayerController JSON.
• Common: PlayerSettingsRepository clamp, playback settings slider, player event subtitleOutlineWidthDelta, English strings.

Windows native bridge is unchanged (outline apply there still the old path). Android already used outlineWidth in libmpv; the settings slider is now visible on all platforms because the setting is shared.

Issue or approval

No linked issue: fix came from in-app testing of the outline toggle, not a GitHub issue. Happy to file one if maintainers want it linked.

UI / behavior impact

• No UI change
• No behavior change
• UI changed only to fix a documented glitch/bug
• Behavior changed only to fix a documented bug/regression
• UI change has explicit maintainer approval
• Behavior change has explicit maintainer approval

UI: outline width stepper in the player Style panel and a matching settings slider. No layout/theme redesign.

Policy check

• I have read and understood CONTRIBUTING.md.
• This PR is small, focused, and limited to one problem.
• This PR is scoped to the desktop app, desktop packaging, desktop documentation, or shared code required for desktop behavior.
• This PR is not cosmetic-only.
• Any UI change fixes a linked glitch/bug and includes visual proof, or this PR has no UI change.
• Any behavior change fixes a linked bug/regression or has explicit approval, or this PR has no behavior change.
• This PR does not bundle unrelated refactors, cleanups, formatting, or drive-by changes.
• This PR does not add dependencies, architecture changes, migrations, or product-direction changes without explicit approval.
• I listed the testing performed below.

No GitHub issue yet (see above). Screenshots/video not attached in this description.

Scope boundaries

• Did not change Windows player_bridge.cpp.
• Did not change iOS/Android native apply beyond shared settings UI.
• Custom styling Off (libass) still uses embedded ASS styles; outline controls stay ignored there.
• No dependency, packaging, or architecture changes.

Testing

Manual intent (macOS desktop, custom styling On):

• Outline Off — border gone
• Outline On — border back
• Width 1–8 in player and Settings → Playback; persists after reopen
• Bold + outline together
• Custom styling Off still looks like embedded ASS
• Background color + outline still readable

Screenshots / Video

Not attached. UI addition is the outline width stepper/slider next to the existing outline toggle.

Breaking changes

None for config/schema. Possible visual diffs only with custom styling On:

• Shadow=0 can flatten ASS drop shadows.
• Forced Outline= can change thickness vs the file’s embedded outline.
• Stored outline width outside 1–8 is clamped.

Linked issues

No linked issue — outline toggle was broken on macOS in the player Style panel; width control uses the existing outlineWidth setting.