Add cross-platform yt-dlp resolution without breaking Windows builds

[Copilot]

Reviewed PR #2 (cross-platform macOS/Linux support). The core refactoring is sound but contains a breaking change for Windows: extraResources.from was changed from "bin" to "electron/bin", which mismatches getBundledBinaryPath() resolving to <project_root>/bin/ — packaged Windows builds would fail to find yt-dlp.exe.

This PR applies the cross-platform changes safely:

• Platform-dispatched ensureManagedYtDlpPath() — winManagedYtDlpPath() preserves the original Windows logic verbatim; unixManagedYtDlpPath() uses which yt-dlp for Linux/macOS
• Did not apply extraResources.from change — keeps "bin" to stay consistent with getBundledBinaryPath()'s dev-mode path (path.join(__dirname, "..", "bin", binaryName))
• Fixed typo from PR Added compatibility for MacOS and Linux. #2: winManagedYtDplPath → winManagedYtDlpPath
• README — added Linux/macOS build prerequisites with proper markdown (PR Added compatibility for MacOS and Linux. #2 had broken nested code blocks)

function ensureManagedYtDlpPath() {
  if (process.platform === "win32") {
    return winManagedYtDlpPath();     // unchanged original logic
  }
  if (process.platform === "linux" || process.platform === "darwin") {
    return unixManagedYtDlpPath();    // resolves via `which yt-dlp`
  }
  throw new Error(`Unsupported platform: ${process.platform}`);
}

PR #2 review summary

Change	Windows-safe?	Action
main.js refactoring	✅	Applied with fixes
extraResources.from: "electron/bin"	❌	Not applied
package-lock.json version bump	—	Already at 1.0.10 on main
README docs	⚠️ broken markdown	Rewritten

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