Improve add reliability: recovery, cancel, and downloads - #7

Make package outcomes drive non-zero exits, isolate staging, roll back partial installs with safe force replace, and classify downloads with cancellable external tools and consistent checksums.

Make package rollback registration-aware, use unique install artifacts, join progress workers on every exit, bound external-process teardown, time-limit error-body drains, and keep rate-limits from advancing candidates.

staticcheck U1000 failed CI on logInstallResultDetails, updateInstallStatus, and installFontsInDebugMode.

… type safety

… error handling

- Removed unused dependency on github.com/blang/semver and updated to use golang.org/x/mod v0.41.0.
- Refactored font installation tests to utilize a new control structure for injecting failure scenarios, enhancing test reliability and clarity.
- Simplified table rendering in various commands by using default column configurations.
- Removed deprecated functions and cleaned up code for better maintainability.

… operations

…ment without overcomplicated backup first

…d correct link paths

…ion handling and track incomplete operations

…V1 to V2 on fontget-sources

…check and family classification.

…tion for tracked files and better cancellation handling. Also Fixed error reporting during removal operations.

Without the deleted cross-platform tests, ubuntu staticcheck flags the helpers as unused (U1000).

…ogress messaging.