Preview the next exercise and count into each set during rests

The run flow's between-exercise rest now previews the next exercise — its
figure and a large "Coming up" name — and the hands-free narration gains a
per-second count-in ("<Exercise>, in 1, 2, 3, GO!") spoken before every set,
plus a "Coming up" announcement as a between-exercise rest begins. A new
Settings > Narration picker chooses the count-in cues, the setup/form read,
or both.

Also fixes spoken cues going silent after the first exercise in a flow split:
the stop-on-teardown moved from the per-exercise view (rebuilt on every
hand-off) to the run host, which stays mounted for the whole run. The audio
session now holds its duck across the per-second count so background music
doesn't pulse between words.

Claude-Session: https://claude.ai/code/session_01BQcEWmAPA78338QuEwRkAh

Workouts/Speech/SpeechSettings.swift

@@ -112,6 +112,35 @@ enum SpeechSettings {
     }
 }
 
+/// What the automatic workout narration says while a flow-mode split runs, chosen in
+/// Settings (only meaningful when "Speak Exercise Cues" is on). Stored as its raw string
+/// under `spokenCueStyle`, read by both the Settings picker and the run flow.
+enum SpokenCueStyle: String, CaseIterable, Identifiable {
+    /// "Coming up, <exercise>" during the rest, then "in 1, 2, 3, GO!" before each set.
+    case cues
+    /// Reads each exercise's setup & form script aloud when it starts (the original behavior).
+    case instructions
+    /// Both — the concise coming-up/countdown cues plus the setup & form read.
+    case both
+
+    var id: String { rawValue }
+
+    /// Picker label.
+    var displayName: String {
+        switch self {
+        case .cues: "Coming Up & Countdown"
+        case .instructions: "Setup & Form Read"
+        case .both: "Both"
+        }
+    }
+
+    /// Whether this style speaks the concise "coming up" / "1, 2, 3, GO!" cues.
+    var speaksCues: Bool { self == .cues || self == .both }
+
+    /// Whether this style reads each exercise's setup & form script on start.
+    var readsInstructions: Bool { self == .instructions || self == .both }
+}
+
 private extension AVSpeechSynthesisVoiceQuality {
     /// Orders the quality tiers for "best available" selection and picker sorting.
     var rank: Int {