Add canonical audio preparation and meeting context support

PROJECT_KNOWLEDGE.md

@@ -25,6 +25,13 @@ Implemented:
 - Prompt loading from `src/meeting_lab/llm/prompts.py`.
 - Meeting Context V1 loading, validation and optional extraction prompt
   injection with minimal extraction JSON provenance.
+- FFmpeg-backed WAV, FLAC and M4A preparation into a per-run canonical mono
+  16 kHz signed PCM16 WAV artifact before transcription or diarization. Audio
+  preparation always runs. Optional loudness normalization defaults to on and
+  currently uses the isolated FFmpeg filter
+  `loudnorm=I=-16:LRA=11:TP=-1.5`. This is a conservative speech-recording
+  default and may be revisited after empirical comparison without changing the
+  orchestration API.
 - Interim Markdown protocol generation in `src/meeting_lab/protocol/`.
 - Non-LLM unit tests for chunking, extraction helpers, protocol rendering and
   gold-test runner validation.
@@ -139,6 +146,9 @@ departments only when they are explicitly supplied as metadata. It must not be
 used to infer responsibilities. In the current implementation this context can
 be injected into chunk extraction prompts as authoritative metadata, and only
 minimal provenance is written to extraction JSON.
+The implemented MVP statuses are exactly `present` and `mentioned_only`.
+Legacy entries without a status receive collection-appropriate defaults. Only
+present participants may be targets of explicit `SPEAKER_XX` mappings.
 
 A `responsible` or future `owner` / `assignee` value may be recorded only when
 source evidence explicitly assigns, accepts or confirms responsibility. If the