Speaker corrections: rename / merge / reassign + voice learning

Native editor to fix speaker-ID errors after transcription (modeled on recap-relay's
correction UX): rename a speaker in the legend, merge two speakers, or reassign an
individual transcript line. Saving rewrites speakers.json, re-renders transcript.md +
recap.html, and updates the voiceprint memory — so a correction compounds: naming an
"Unknown" speaker teaches that voice for future calls.

- SpeakerEditing (pure, tested): replaceSpeaker (rename = merge-onto-existing),
  reassign, netNameMap (compose ops), and remap (apply a name map to a recap's
  structured fields + whole-word free text, so summaries/extras update without re-LLM).
- RecapEditModel (@MainActor): loads speakers.json (+ optional recap.json +
  cluster_fingerprints.json); on save writes the resolved speakers.json, re-renders,
  and reconciles voiceprints — merge keeps the survivor's print; rename/name-an-Unknown
  enrolls the cluster's fingerprint under the new name.
- TranscriptEditorView (SwiftUI) + EditorWindow (AppKit window for the LSUIElement app);
  menu gains "Edit speakers".
- Pipeline now persists cluster_fingerprints.json (every cluster incl. Unknown) and
  recap.json (RecapFile) so the editor can learn voices + re-render offline.
- RecapModels made Codable; TranscriptAssembler exposes allFingerprints;
  VoiceprintStore gains enroll() + merge().

52/52 XCTest (6 new, incl. a full rename→artifacts→voiceprint round-trip on disk).

Ten31Transcripts/UI/MenuBarView.swift

@@ -94,6 +94,9 @@ struct MenuBarView: View {
                     if let recap = session.recapURL {
                         Button("Open recap") { NSWorkspace.shared.open(recap) }
                     }
+                    if session.canEditSpeakers {
+                        Button("Edit speakers") { session.editLastSession() }
+                    }
                     Spacer()
                 }
                 if !transcriptText.isEmpty {