Add spoken exercise instructions (on-device TTS)

Speak exercise setup and form cues aloud with AVSpeechSynthesizer:

- Library detail: a speaker toolbar button reads the full reference aloud.
- Active workout: an opt-in "Speak Exercise Cues" setting speaks a brief
  cue (Setup/Execution/Cues) when an exercise starts, hands-free.
- Settings › Voice: pick the voice (auto-prefers an installed enhanced/
  premium English voice), a premium-download nudge shown only while on a
  basic voice, and a Speed/Pitch/Volume sheet with Reset to Defaults.

On-device and offline; ducks other audio rather than stopping it. iPhone
only for now. Shared SpeechSettings is the single source of truth for the
voice/prosody, read fresh per utterance so changes preview live.

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

Workouts/ExerciseFigure/ExerciseInfo.swift

@@ -62,6 +62,38 @@ struct ExerciseInfo {
 }
 
 extension ExerciseInfo {
+    /// Sections read aloud in the brief hands-free cue (the workout-flow announcement).
+    /// The library's Speak button reads everything; a mid-workout cue skips the reference
+    /// sections (Common Mistakes, Progression) you don't need with the bar in your hands.
+    private static let briefSectionTitles: Set<String> = ["Setup", "Execution", "Cues"]
+
+    /// Render this exercise as a plain-text script for `AVSpeechSynthesizer`: the name,
+    /// the summary, then each section's title and items as sentences. `brief` keeps only
+    /// the hands-free sections (`briefSectionTitles`), falling back to every section when
+    /// none of them are present, so an exercise with only unusual headings still speaks.
+    func spokenScript(name: String, brief: Bool) -> String {
+        var parts: [String] = [name]
+
+        let summaryLine = summary.replacingOccurrences(of: "\n", with: " ")
+        if !summaryLine.trimmingCharacters(in: .whitespaces).isEmpty {
+            parts.append(summaryLine)
+        }
+
+        var chosen = brief ? sections.filter { Self.briefSectionTitles.contains($0.title) } : sections
+        if chosen.isEmpty { chosen = sections }
+
+        for section in chosen {
+            parts.append(section.title)
+            parts.append(contentsOf: section.items.map(\.text))
+        }
+
+        return parts
+            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
+            .filter { !$0.isEmpty }
+            .map { $0.hasSuffix(".") || $0.hasSuffix("!") || $0.hasSuffix("?") ? $0 : $0 + "." }
+            .joined(separator: " ")
+    }
+
     /// Parse the library's `info.md` shape. Hard-wrapped lines are rejoined: a line
     /// that doesn't start a new block (heading, list marker, blank) continues the
     /// previous one, matching how Markdown renders soft breaks.