feat(usage): exclude daily breaks from the 5h pace marker

[neumie]

What

Adds a Breaks preference (shared between the Claude and Codex usage widgets): recurring daily time ranges that are excluded from the 5-hour pace marker.

On hour windows the marker now paces the budget over worked time — elapsed / (window − breaks inside it) — so it runs at a steady faster rate than the clock and reaches 100% before reset by the break amount. Net effect: a break leaves you more headroom while you work (you have fewer working hours to spend the same budget). Day/weekly windows are untouched (they keep the working-days reshape).

5h window 09:00–14:00, 1h break 12:00–13:00
 time   clock   marker
 10:00   20%     25%
 12:00   60%     75%
 13:00   80%    100%   ← full once worked hours are spent
 14:00  100%    100%

UI

A stepper-based Breaks section (add / remove, 15-min nudges) in both the Claude and Codex settings panels, writing to the shared usage settings blob alongside working-days (merge-preserving).

Notes

• Break coverage is computed with calendar arithmetic (DST-safe across the 23h/25h transition days), and overlapping/duplicate ranges are merged so they can't double-count.
• Stepper clamp bounds are ordered defensively and from_value drops sub-15-min ranges, so a hand-edited/legacy blob can't panic the editor.
• Includes fix(extensions): ExtensionSettingsStore::update now notifies global observers, so a settings change reaches the live widgets immediately instead of on the next poll tick (also benefits working-days).
• 19 unit tests (pace math, overlap merge, DST, validation) pass under UTC/Prague/New_York; workspace clippy clean.

🤖 Generated with Claude Code