fix(download): require aria2 for file transfers

Update yt-dlp to 2026.07.04 and refresh the bundled macOS runtime plus engine locks.

Route every non-media download through aria2 by removing the native HTTP fallback path, native GID handling, and the old direct-download harness.

Retry transient aria2 startup/RPC failures before failing, then show the real last error in the download row and Properties modal so Windows failures are diagnosable instead of silent.

Refresh docs and tests around the aria2-only file-download contract, and advance the Firefox extension submodule to its published wording cleanup.

README.md

@@ -62,7 +62,7 @@ Download the latest desktop build from [GitHub Releases](https://github.com/nimb
 | **Windows x64** | NSIS `.exe` installer | Unsigned. Windows SmartScreen may warn until code signing is added. |
 | **Linux x64** | `.AppImage` | Make executable before launching if your desktop environment does not do that automatically. |
 
-Production bundles include the required media engines for the target platform. Users do not need to install aria2, yt-dlp, FFmpeg, Deno, Python, Homebrew, or a package manager for normal app usage.
+Production bundles include the required media engines for the target platform. Users do not need to install aria2, yt-dlp, FFmpeg, Deno, Python, Homebrew, or a package manager for everyday app usage.
 
 ## Browser Extension
 
@@ -74,7 +74,7 @@ Firelink Companion connects your browser to the desktop app so links and browser
 
 What it adds:
 
-- **Automatic capture** for normal browser downloads, while still routing every captured link through Firelink's Add window.
+- **Automatic capture** for ordinary browser downloads, while still routing every captured link through Firelink's Add window.
 - **Context-menu actions** for "Download with Firelink" and selected links.
 - **Signed local requests** using the pairing token from **Settings -> Integrations**.
 - **Server identity checks** so the extension only trusts the real local Firelink app.