Prepare v1.0.0-rc.1

[enaboapps]

Closes #661

Summary

• set the frontend, Tauri app, Rust crate, startup launcher, browser fallback, and configuration-test versions to 1.0.0-rc.1
• update npm and both Rust lockfiles for the release candidate
• leave the stable v1.0.0 release out of scope

Validation

• npm run lint
• npm test (74 frontend tests and 5 updater-feed tests)
• npm run build
• npm audit --audit-level=high
• full formatting, Clippy with warnings denied, and tests for the app, updater verifier, and startup launcher
• cargo audit 0.22.2 for all three lockfiles
• 229 Rust unit tests and 7 configuration tests
• unsigned Windows UIAccess NSIS build and package verification at version 1.0.0-rc.1

After merge, an annotated v1.0.0-rc.1 tag will be created from main and the signed release workflow will be verified before this issue and milestone are closed.