`gitmastery progress sync on` should report errors appropriately

[jovnc]

Context / Background

Reference forum thread: NUS-CS2103-AY2627-S1/forum#22

When executing gitmastery progress sync on, underlying errors encountered during execution (such as GitHub CLI authentication issues, missing permissions, or network/git push failures) are currently swallowed silently or not adequately reported to the user. This leaves users unaware of sync failures or makes debugging difficult.

Expected Behavior

• Error Visibility: Any errors encountered during the sync enablement process should be captured and surfaced clearly to the user via standard error/output.
• Actionable Guidance: Provide clear diagnostic feedback indicating the root cause (e.g., missing GitHub authentication, insufficient token scope, or network/remote errors) and suggested steps to resolve it.
• Exit Status: Ensure the CLI exits with an appropriate non-zero exit code when the operation fails.

Steps to Reproduce

1. Trigger an error condition (e.g., logged out of gh, revoked scopes, or disconnected network).
2. Run gitmastery progress sync on.
3. Observe that errors are suppressed rather than surfaced with clear diagnostic messages and proper exit codes.