[Sternpaul]

What this PR does

Adds a Live Activity for a live-tracked workout (a run, ride, walk, or any sport started from the workout picker) on the Lock Screen and in the Dynamic Island.

• Lock Screen: sport, live heart rate, duration, GPS distance and average pace. A workout with no route shows duration and heart rate only.
• Dynamic Island: sport icon and clock (compact leading), pace or HR (compact trailing), all three figures (expanded).

It is its own activity type (WorkoutActivityAttributes) with its own switch, Settings › Live notifications › Workout (on by default), so it works with the Live HR banner turned off. While it shows, the Live HR banner steps aside and a sync starts no new banner, the same as for a Lift Log session.

Details:

• The clock is Text(.timer) from the start time shifted by paused time, so iOS counts it up by itself between pushes. While paused it shows the frozen active time.
• Labels are localized and distance/pace formatted in the user's units on the app side, because the widget extension has no string catalog or unit prefs. The one new Settings string has translations for every catalog locale.
• Pushes: pause/resume immediately; changed HR, distance or pace at most every 5 s.
• AppModel.activeWorkoutIsGps becomes private(set) so the banner uses the same GPS check as the live workout screen's distance row.

iOS only: Live Activities have no Android counterpart. An ongoing-notification equivalent could follow separately.

Overlap with #2761

#2761 also adds a workout Live Activity (Start/Pause/Resume/End controls and a clock, part of training favorites). It does not show distance, pace or heart rate, which is the focus here. Both PRs use the names WorkoutActivityAttributes / WorkoutLiveActivity, so whichever lands second needs adapting. I'm happy to rebase on top of #2761 and move distance, pace and heart rate into its TrainingDisplay, or to keep this PR standalone, whichever the maintainers prefer.

Type of change

• New feature

How it was tested

• Built with the fork's "Testing build (fork)" workflow and sideloaded on an iPhone with a WHOOP 5.0.
• Started a Running workout and locked the phone: the banner showed sport, live HR, a ticking duration, distance and pace (screenshots below).
• Paused and resumed mid-workout: the banner showed "Paused" with the clock frozen, then resumed counting from the right active time.
• Tools/i18n_audit.py --ci and Tools/doc_comment_lint.py report nothing new.

Screenshots

Lock Screen while running:

Paused:

Dynamic Island (compact), before the first pace:

Checklist

• UI changes use only StrandDesign tokens
• No hardcoded hex frame bytes; no BLE changes
• Follows the conventions in docs/CONTRIBUTING.md
• I did not commit generated output (Strand.xcodeproj/) or any secrets/keystores

Related issues

Refs #757
Refs #1195