feat(settings): deep links into Settings panes (WW-53)

[nathanialhenniges]

Closes WW-53.

What

wolfwave://settings/<pane>[/<section>] opens Settings at a named pane, scrolls to the tagged card, and flashes it with an accent ring. Works whether Settings is closed or already open on another pane. Anything unknown falls back to the General pane; an unknown section on a known pane keeps the pane and skips the scroll.

• wolfwave scheme registered in Info.plist (CFBundleURLTypes), received in AppDelegate.application(_:open:).
• Core/SettingsDeepLink.swift: pure nonisolated parser + urlString inverse. Pane ids are new stable kebab-case SettingsSection.slug values, never the visible titles. Section slugs restricted to [a-z0-9-]+.
• Core/SettingsNavigation.swift: @MainActor @Observable hand-off (pending / highlighted) consumed by SettingsView; one ScrollViewReader reaches every pane, including ones that own their own ScrollView. Each new link cancels the previous in-flight scroll task, and highlight expiry lives in SettingsView so a slug with no mounted anchor still clears.
• Views/Shared/DeepLinkAnchor.swift: .deepLinkSection("slug") scroll target + fading accent ring; 30+ anchors tagged across all panes. Catalog entry added.
• Removed the old Twitch-only selectedSettingsSection UserDefaults hint (key, Preferences accessors, AppConstants.Twitch/Discord.settingsSection); its two callers now route through navigateSettings(to:). This also fixes pane selection when the window is already open.

Full pane/section table: Settings docs → Deep links (settings.mdx in this PR).

Testing

• SettingsDeepLinkTests (new): slug stability/uniqueness, round-trips, case + trailing-slash tolerance, every fallback path.
• Full unit suite run pre-rebase (1364 tests; only the known parallelism flakes in SkipVoteManagerTests etc., all pass in isolation). Post-rebase: build + SettingsDeepLinkTests + AppConstantsTests green.
• Live-verified on the Dev app: warm delivery, cold launch via URL, fallback to General, on-screen scroll + ring flash.
• Codex CLI review run; fixes folded in (CFBundleTypeRole, slug-only logging, stale-task cancellation, highlight expiry).

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