Prepare v1.0.0-beta.12 prerelease

[enaboapps]

Summary

• bump Switchify PC to 1.0.0-beta.12 across package, Tauri, Cargo, startup launcher, browser fallback, and configuration-test metadata
• prepare the prerelease containing the Remote keyboard shortcut injection fix from Fix Remote keyboard shortcut injection #647

Validation

• npm run lint
• npm test (74 Vitest tests and 5 release-feed tests passed)
• npm run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --check
• cargo clippy --locked --manifest-path src-tauri/Cargo.toml --all-targets -- -D warnings
• cargo test --locked --manifest-path src-tauri/Cargo.toml (217 unit tests and 2 config tests passed)
• confirmed all managed version locations are 1.0.0-beta.12 and no beta.11 value remains in the release set

Closes #648