Build/windows aether fetch helper

[Nishef1]

Summary

Add a first-class PowerShell helper for fetching the pinned Aether core on Windows and reuse that helper in the Windows build job.

This removes duplicated inline download logic from CI and gives Windows contributors the same one-command, checksum-verified setup path already available to Linux/macOS contributors.

Problem

The repository currently has a reusable Unix fetch helper, while Windows setup is split between:

• manual download instructions for local development; and
• a separate inline PowerShell implementation embedded in the GitHub Actions workflow.

That duplication makes the Windows local-development and release-build paths easier to drift apart.

Changes

• add src-tauri/binaries/fetch-aether.ps1
• keep the helper pinned to the repository's current Aether release (v1.3.0)
• enable TLS 1.2 for compatibility with Windows PowerShell 5.1 on older systems
• retry transient downloads with bounded backoff
• download both the Windows x64 archive and the published SHA256SUMS.txt
• verify SHA-256 before extracting or replacing the local executable
• stage the prepared executable before replacing aether.exe, so failed downloads/checks do not overwrite the existing binary
• clean up temporary download/extraction files
• replace the duplicated inline Windows download block in .github/workflows/build.yml with the helper call
• update English and Persian build instructions to document both platform-specific helpers

Why

The same core-preparation logic should be reusable by local development and CI. Keeping checksum verification in one Windows helper reduces duplicated release plumbing and makes clean Windows setup less error-prone.

Scope

This is build/setup tooling only. It does not introduce runtime core updates, change the pinned Aether version, or modify any tunnel/protocol behavior.

Validation

• compared against upstream main at 9ba2ef0: four focused files changed
• reviewed the helper against the existing pinned Unix fetch flow and the current Windows CI checksum-verification behavior
• verified that CI still fetches the Aether core before dependency installation and Tauri packaging

PowerShell was not available in the connector environment used to prepare this branch, so the helper has not been executed there. Please run the repository checks and exercise fetch-aether.ps1 on Windows before marking the PR ready.