Publish dual-architecture macOS assets and select the matching update

[Infiland]

Child scope of #736. Depends on #856.

Problem

Release publication, recovery/audit policy, checksums, documentation, and the runtime update checker all assume one generic macOS ZIP/DMG pair. Once native arm64 and x86_64 builds exist, those assumptions can drop a variant or offer users the wrong executable.

Scope

• Replace the generic macOS payload pair with exactly four architecture-specific files:
  • GM2Godot-macos-arm64.zip
  • GM2Godot-macos-arm64.dmg
  • GM2Godot-macos-x86_64.zip
  • GM2Godot-macos-x86_64.dmg
• Update release artifact extraction, checksum generation, release publisher/recovery ownership, existing-release integrity checks, asset-digest auditing, and tests to require six payloads plus SHA256SUMS exactly once.
• Reject stale generic macOS names and partial/duplicate architecture inventories.
• Make the update checker map the normalized host machine to one exact ZIP suffix; unsupported/ambiguous machines must fall back safely to the release page rather than choosing the first macOS asset.
• Update README, Wiki installation/maintenance/compatibility guidance, and release notes to state arm64 and x86_64 support with macOS 15.0+.
• Close parent Publish verified Apple Silicon and Intel macOS builds #736 only after an exact-main release contains and validates both variants.

Acceptance criteria

• Release publication requires exactly seven assets: six payloads and one checksum manifest.
• SHA256SUMS contains exactly the six expected architecture-specific payload names and verified digests.
• Existing-release/recovery logic rejects missing, extra, duplicate, generic, or cross-architecture macOS assets.
• arm64 hosts select only the arm64 ZIP; x86_64 hosts select only the x86_64 ZIP; unknown hosts do not auto-download either.
• README, Wiki, and release notes consistently state macOS 15.0+, Apple Silicon, Intel, and the lack of Developer ID trust until Developer ID sign and notarize macOS release artifacts #737 is complete.
• Linux and Windows release names/content remain unchanged.
• Pyright, Ruff, focused publisher/update/workflow/documentation tests, and the full unit suite pass.

Non-goals

Do not merge finished PyInstaller applications into a universal binary and do not add Developer ID signing, notarization, or stapling here.