added time tool with jitter

In-app update check + GitHub Actions release workflow

App polls GitHub Releases on launch (throttled to once per 12h)
and prompts the user when a newer signed APK is available. The
prompt's "Download" button opens the APK URL in a browser; the
system installer takes over from there. "Later" suppresses that
exact version until a newer one ships. Repo is wired via
BuildConfig.GITHUB_REPO (defaults to wannabeepolymath/gps-
simulation, override with -Pgithub.repo at build time).

Releases workflow (.github/workflows/release.yml): triggered on
tag push v* (or manual dispatch), decodes a base64 keystore from
secret, runs assembleRelease with all signing + config props
injected from secrets, attaches gps-simulator-<tag>.apk to the
release, and uses GitHub's auto-generated release notes.

Required repo secrets: KEYSTORE_BASE64, KEYSTORE_PASSWORD,
KEY_ALIAS, KEY_PASSWORD, GOOGLE_WEB_CLIENT_ID, API_BASE_URL.