fix(security): use HTTPS for CLI binary download URL (#12)

F-001 / DEVA11Y-473 — The default download URL used plaintext HTTP
(CWE-319), allowing MitM to substitute a malicious binary.
Switch to HTTPS to enforce TLS.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sunny-se

Plugins/BrowserStackAccessibilityLint/BrowserStackAccessibilityLint.swift

@@ -339,7 +339,7 @@ private struct BrowserStackCLIDownloader {
     private func defaultDownloadURL() throws -> URL {
         let os = try currentOSName()
         let arch = try currentArchName()
-        guard let url = URL(string: "http://api.browserstack.com/sdk/v1/download_cli?os=\(os)&os_arch=\(arch)") else {
+        guard let url = URL(string: "https://api.browserstack.com/sdk/v1/download_cli?os=\(os)&os_arch=\(arch)") else {
             throw PluginError("Failed to create download URL for \(os) \(arch).")
         }
         return url