Add Docker support, fix stale docs, translate UI to English

- Dockerfile + docker-compose.yml: two services (recorder + web) sharing
  ./recordings bind mount; recorder maps /dev/snd for ALSA soundcard access
- requirements.txt: requests, numpy, soundfile
- .dockerignore, updated .gitignore (add __pycache__, .pytest_cache)
- isr.py: add SIGTERM handler for clean Docker shutdown; fix stale error
  message that referenced removed PulseAudio/PipeWire/PortAudio backends
- web.py: translate all German UI strings to English
- config.example.ini: remove PipeWire/PulseAudio/PortAudio backend refs,
  simplify soundcard tips to ALSA only
- README.md: full rewrite as user guide (quick start, config reference,
  Docker notes, how it works)
- CLAUDE.md: update architecture section to reflect ALSA-only backend
- Delete changelog.txt and guide.md (internal session notes)

docker-compose.yml

@@ -0,0 +1,19 @@
+services:
+  recorder:
+    build: .
+    volumes:
+      - ./config.ini:/app/config.ini:ro
+      - ./recordings:/recordings
+    # Soundcard (ALSA) access — comment out if you only record streams
+    devices:
+      - /dev/snd:/dev/snd
+    restart: unless-stopped
+
+  web:
+    build: .
+    volumes:
+      - ./recordings:/recordings:ro
+    ports:
+      - "8080:8080"
+    restart: unless-stopped
+    command: ["python", "web.py", "--dir", "/recordings"]