Give the exercise run screen its own chrome, rolling digits, and a true resume

The run screen now hides the navigation bar in both orientations and draws
its own header — back chevron top-left, exercise name (plus library name
when renamed) in large type where the toolbar was, previewing the next
exercise during a between-exercise rest. Work and rest counters are pinned
to the exact vertical center of the timer half via equal flexible bands,
with the adjust pill moved to an overlay so complications can't shift them.
Counter digits are now state-driven and roll through numericText
transitions (work count-up, rest countdown, and the Done button count).

Reopening an in-progress exercise now resumes its timer from the durable
timestamps instead of restarting at zero: no sets done anchors the
stopwatch to startedAt; mid-rest lands back on the rest page with the
countdown still running off its true window; past the window the next
set's stopwatch counts from the rest's computed end. The resume page is
computed at init because the paged TabView must initialize on it — a
post-layout backward jump wedges the pager, which then ignores the next
animated programmatic advance.

Claude-Session: https://claude.ai/code/session_01H8VxUX4ckjU3vRF5M4L5FV

CHANGELOG.md

@@ -1,5 +1,13 @@
 **July 2026**
 
+The exercise screen now shows the exercise name in large type with a simple back chevron in place of the toolbar, in portrait and landscape alike.
+
+Work and rest counters now sit at the exact same spot on screen, so the digits no longer shift between phases.
+
+Timer digits now roll smoothly as they count up or down.
+
+Reopening an exercise that's already underway now continues its timer where it left off — even mid-rest — instead of restarting from zero.
+
 A routine can now include the same exercise more than once — swipe right on an exercise to duplicate it for interval-style segments.
 
 Exercises can now be renamed per routine, like "Warmup Walk" for a treadmill segment, while their animated figure and guide still follow the original exercise.