Add bettercapture:// URL scheme for external automation

[qlaffont]

Summary

Add a `bettercapture://` URL scheme so external tools (Raycast, Shortcuts, Alfred) can trigger recording actions without simulating keyboard shortcuts.

Motivation

BetterCapture currently exposes control only via user-configured global keyboard shortcuts. External automation tools must relay keystrokes via Accessibility APIs, which:

• Requires extra permissions
• Fails if the user has not configured a shortcut
• Cannot reliably open a custom output folder (security-scoped bookmarks)

Proposed URLs

URL	Action
`bettercapture://toggle`	Same as Toggle Recording shortcut (`toggleRecording()`)
`bettercapture://open-recordings`	Same as Open Output Folder menu action

Implementation sketch

1. Register `bettercapture` in `Info.plist` (`CFBundleURLTypes`)
2. Handle URLs in `BetterCaptureApp.swift` via `.onOpenURL`, calling existing `RecorderViewModel` / `SettingsStore` methods

No new ViewModel API needed — wire to existing keyboard shortcut and menu bar handlers.

Use case

I am building a Raycast extension for BetterCapture. Phase 1 uses shortcut relay; Phase 2 would switch to URL scheme once available upstream.

Happy to contribute a PR if this direction is approved.