Prepare Hronomancer 1.2.0 with automatic updates

[Hronom]

Summary

• add automatic startup update checks with native notifications and tray actions
• prepare the 1.2.0 version and release notes
• restore clean installs and type-checking with compatible Vite and TypeScript versions
• harden release validation, updater metadata checks, and Dependabot compatibility guards
• migrate Snap packaging to the supported core22 snapcraft configuration

Why

Hronomancer did not check for new releases automatically. Recent Vite 8 and TypeScript 7 upgrades also exceeded the peer ranges supported by the current Electron/Vue toolchain, breaking clean npm ci and the full type-check. The release workflow additionally needed stronger tag/version and updater-metadata validation.

Impact

Packaged builds check GitHub Releases shortly after startup. Windows and supported Linux packages can download and install updates from the tray or notification; package-manager-owned formats stay under system control, and unsigned macOS builds open the release downloads instead of attempting unsupported in-app installation.

Validation

• clean npm ci under Node 24.14.0
• npm test — 4/4 passing
• npm run build — full renderer, preload, and main-process type-check/build passing
• npm audit --omit=dev — 0 production vulnerabilities
• built x64/ARM64 AppImage, DEB, and RPM artifacts plus x64 Snap
• validated both Linux updater manifests and both packaged app archives
• confirmed v1.2.0 is unused and the repository has no open issues

Unfiltered npm audit findings are confined to electron-builder's upstream build-time dependency tree; the packaged production audit is clean.