Establish initial project architecture

docs/adr/0003-use-pyannote.md

@@ -0,0 +1,25 @@
+# ADR 0003: Use pyannote for Speaker Diarization
+
+## Status
+
+Accepted
+
+## Context
+
+The project requires speaker diarization to assign transcript segments to speakers.
+
+The first implementation should provide reliable separation of speakers in meetings, while keeping the diarization component replaceable.
+
+## Decision
+
+The project will use `pyannote.audio` as the initial speaker diarization engine.
+
+Speaker diarization will be treated as a separate pipeline step after transcription.
+
+## Consequences
+
+- Diarization can be improved or replaced independently from transcription.
+- Speaker labels are derived metadata and must not modify the canonical transcript.
+- Human correction of speaker names should be supported later.
+- The diarization module must hide the concrete engine behind an internal interface.
+- Model name, engine version and timestamp should be stored with every diarization result.