Let routines rename exercises and repeat them for interval segments

An exercise's name is now a per-routine display name: a new optional
libraryName on ExerciseDocument (snapshotted onto WorkoutLogDocument at
plan time) keeps the link to the bundled library exercise, and every
figure/info/cue lookup resolves libraryName ?? name. Deliberately not
schema-bumped — an older app dropping the key only strands the
figure link, same rationale as activityType. Cache schema bumped to 9
for the new columns.

The picker no longer filters out exercises already in the routine
(an "×N" badge marks them instead), exercise rows gain a leading
Duplicate swipe that clones an entry in place, and the edit sheet gets
a Name field with the library exercise shown read-only above it.

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

README.md

@@ -14,7 +14,9 @@ your own iCloud Drive.
   (Upper Body / Core / Lower Body machine routines, plus an equipment-free
   **Bodyweight Core** circuit with its own warm-up) appear automatically on first
   launch; editing one makes it your own copy, and deleted starters can be restored
-  from Settings.
+  from Settings. Any exercise can be duplicated and renamed for this routine only
+  (its figure and guide still come from the original) — build an interval routine
+  like a treadmill's Warmup / Brisk Walk / Cooldown from one library exercise.
 - **Exercise library** — a bundled library of 67 exercises to populate your
   splits, authored in `Exercise Library/` with per-exercise setup, cues,
   mistakes, progressions, and an anatomically-rigged 3D stick-figure visual