feat(sync): show worker progress during sync

[vicentereig]

Summary

Show what a long-running sync is doing while it runs.

The progress block now shows:

• aggregate activity, GPX, health, and performance totals
• one row for each producer (P) fetching from Garmin
• one row for each consumer (C) writing locally
• task id, item, current state, and elapsed time

Example:

Act 120/1223 | GPX 80/993 | Health 400/4228 | Perf 90/604 | elapsed 2m 41s
P0  Activities #4855  200-250                  fetching           3s
P1  Health     #4236  2015-01-12               rate limit wait     8s
C0  GPX        #4839  2026-03-17 Run           writing             1s

Scope

This is intentionally limited to the UI for issue #17. It does not change queue claiming, retry semantics, stale-claim ownership, logging, timeout policy, or resume behavior from #18.

Closes #17.

Validation

• cargo fmt --all -- --check
• cargo test -p garmin-cli
• cargo clippy -p garmin-cli --all-targets --all-features -- -D warnings