feat: implement full-platform STT API (v2.3 consensus plan)

Batch+realtime transcription API: faster-whisper engine w/ EngineOwner
(single GPU owner, OOM downgrade chain, persisted attempted_profiles),
hardware-adaptive device manager (T0-T3 VRAM tiers), Redis/in-proc job
queue w/ leases + crash recovery, postprocess (glossary/rules/LLM w/
egress guard), privacy-first result store (UUID keys, source deleted
after transcribe), retention sweeper, API-key auth (HMAC digests,
scopes, job ownership), WebSocket realtime lane (LocalAgreement),
CLI (detect/transcribe/bench/serve/key), Docker, benchmark runner.

127 mock-based tests pass; ruff clean. Includes verification checklist
and autoplan review notes.

docker/Dockerfile.cpu

@@ -0,0 +1,20 @@
+# luke_scribe CPU 이미지
+FROM python:3.12-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends ffmpeg \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+COPY pyproject.toml README.md ./
+COPY src/ ./src/
+
+RUN pip install --no-cache-dir -e ".[engine,api]" \
+    && pip install --no-cache-dir "faster-whisper>=1.0.3"
+
+ENV LUKESCRIBE_DEVICE=cpu \
+    LUKESCRIBE_QUEUE_BACKEND=redis \
+    LUKESCRIBE_HOST=0.0.0.0 \
+    LUKESCRIBE_PORT=8000
+
+EXPOSE 8000
+CMD ["python", "-m", "luke_scribe.cli", "serve"]