Revert adjacent same-speaker segment collapse

User found the merged transcript lines harder to read — too many sentences
joined into one statement. Remove SpeakerReconciler.mergeAdjacent, its wiring in
finishBackend (restore the no-LLM early return), and its tests. Back to one
segment per diarized utterance.

Ten31Transcripts/Session/SpeakerReconciler.swift

@@ -82,28 +82,6 @@ enum SpeakerReconciler {
                             speakers: speakers, segments: result, models: file.models)
     }
 
-    /// Collapse consecutive segments from the SAME speaker separated by ≤ `maxGap`
-    /// seconds into one, joining their text — so fragments reabsorbed by smoothing
-    /// (e.g. "I" then "need to switch it back") read as a single clean line. Pure.
-    static func mergeAdjacent(_ file: SpeakersFile, maxGap: Double = 2.0) -> SpeakersFile {
-        let sorted = file.segments.sorted { $0.start < $1.start }
-        guard !sorted.isEmpty else { return file }
-        var out: [SpeakersFile.Segment] = []
-        for s in sorted {
-            if var last = out.last, last.speaker == s.speaker, s.start - last.end <= maxGap {
-                let joined = [last.text, s.text].compactMap { $0?.trimmingCharacters(in: .whitespaces) }
-                    .filter { !$0.isEmpty }.joined(separator: " ")
-                last = .init(start: last.start, end: max(last.end, s.end), speaker: s.speaker,
-                             text: joined.isEmpty ? nil : joined)
-                out[out.count - 1] = last
-            } else {
-                out.append(s)
-            }
-        }
-        return SpeakersFile(sessionId: file.sessionId, app: file.app, durationSec: file.durationSec,
-                            speakers: file.speakers, segments: out, models: file.models)
-    }
-
     // MARK: - Voiceprint merge (pure)
 
     static func protectedNames(_ file: SpeakersFile, selfName: String) -> Set<String> {