Release SAID 0.4.0 for macOS

[supdub]

What changed

• adds a native AppKit menu-bar build for one-shot local dictation on macOS
• packages a universal Apple Silicon/Intel DMG with the verified four-model bundle and license files
• adds Exact/Clean modes, Japanese/Korean toggles, Accessibility paste with clipboard fallback, and focus-change safety
• adds Developer ID/notarization support plus a clearly labeled ad-hoc-signed preview path
• adds packaged-app self-testing and mounted-DMG verification in GitHub Actions
• bumps the source version to 0.4.0 and documents the first macOS release scope

Why

SAID was Windows-only. This creates the smallest dependable macOS release that reuses the portable local transcription and Clean pipeline while leaving streaming, Adapt, and richer setup UI for later.

Validation

• 5/5 portable CTest suites pass locally
• CMake configuration and build pass on Linux
• macOS build scripts pass Bash syntax checks
• workflow YAML, Info.plist, and entitlements parse successfully
• model hashes match the existing Windows release definitions

The PR's macOS Actions run is the required native compile, packaged-model self-test, universal-binary check, DMG mount, bundle inspection, and code-signature verification.