Polish fleet tab strip glass dock

[NagyVikt]

Summary:

• Render glass dock pill middles with iOS half-circle caps (◖ / ◗) instead of hard vertical edges.
• Add a full-width dark band under the floating dock, with the existing inner shadow layered on top.
• Keep the LIVE chip tick-driven pulse and add focused coverage for the pulse fill.

Verification:

cargo test -p fleet-tab-strip

running 8 tests
test tests::json_number_extracts_counter_without_json_dependency ... ok
test tests::dock_shadow_adds_full_width_dark_band ... ok
test tests::marquee_scrolls_long_focus_text ... ok
test tests::current_focus_prefers_claimed_task_rows ... ok
test tests::live_pill_fill_pulses_by_tick ... ok
test tests::design_e_dock_degrades_to_one_row_header ... ok
test tests::design_e_pills_use_ios_half_circle_caps ... ok
test tests::design_e_dock_renders_all_tabs_and_live_chip ... ok

test result: ok. 8 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s