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)

config.example.ini

@@ -0,0 +1,146 @@
+# ISR - Audio Recorder Configuration
+# Supports multiple recording sources: Icecast streams and soundcards
+#
+# Configuration sections:
+#   [general]     - Shared settings for all sources (optional)
+#   [sourcename]  - One section per recording source (name is your choice)
+#
+# Each source section must have 'type' set to either 'stream' or 'soundcard'
+
+# =============================================================================
+# GENERAL SETTINGS (optional - can be overridden per source)
+# =============================================================================
+[general]
+# Output directory for recordings (will be created if it doesn't exist)
+output_directory = recordings
+
+# Duration in minutes after which to split into a new file
+split_minutes = 60
+
+# Filename pattern with strftime format codes
+# Examples:
+#   %Y%m%d_%H%M%S           -> 20241216_143000.ext
+#   recording_%Y-%m-%d_%H%M -> recording_2024-12-16_1430.ext
+#   %Y/%m/%d/audio_%H%M%S   -> 2024/12/16/audio_143000.ext (creates subdirs)
+# Common codes: %Y=year, %m=month, %d=day, %H=hour, %M=minute, %S=second
+filename_pattern = %Y%m%d_%H%M%S
+
+# Maximum number of connection/recording retry attempts before giving up
+max_retries = 10
+
+# Delay in seconds between retry attempts
+retry_delay_seconds = 5
+
+# Logging level: DEBUG, INFO, WARNING, ERROR, CRITICAL
+log_level = INFO
+
+# Log file location
+log_file = recorder.log
+
+
+# =============================================================================
+# EXAMPLE: ICECAST STREAM SOURCE
+# =============================================================================
+[mystream]
+# Source type (required): stream or soundcard
+type = stream
+
+# Stream URL (required for stream type)
+url = http://example.com:8000/stream
+
+# Authentication (optional - leave empty for public streams)
+username =
+password =
+
+# Audio format: auto (detect from stream), mp3, ogg, aac, flac, opus
+format = auto
+
+# Override general settings for this source (optional):
+# output_directory = recordings/streams
+# split_minutes = 30
+# filename_pattern = mystream_%Y%m%d_%H%M%S
+
+
+# =============================================================================
+# EXAMPLE: SOUNDCARD SOURCE (Linux)
+# =============================================================================
+# Uncomment and configure to record from a soundcard
+#
+# [stereo_mix]
+# type = soundcard
+#
+# # Device selection (use one of these methods):
+# #   device = default    - Use system default input device
+# #   device = monitor    - Auto-select first monitor/loopback source (for system audio)
+# #   device = <name>     - Match device by partial name (e.g., "Stereo Mix")
+# #   device = <id>       - Use exact device ID from --list-devices
+# #
+# # To list available devices, run: python isr.py --list-devices
+# device = default
+#
+# # Audio backend (only 'alsa' is supported):
+# # backend = alsa
+#
+# # Sample rate in Hz (common: 44100, 48000, 96000)
+# sample_rate = 44100
+#
+# # Number of audio channels (1 = mono, 2 = stereo)
+# channels = 2
+#
+# # Output format: wav, flac
+# format = wav
+#
+# # Override general settings for this source (optional):
+# # output_directory = recordings/soundcard
+# # split_minutes = 60
+# # filename_pattern = soundcard_%Y%m%d_%H%M%S
+
+
+# =============================================================================
+# MULTIPLE SOURCES EXAMPLE
+# =============================================================================
+# You can define as many sources as you want. Each will record simultaneously.
+#
+# [radio_station_1]
+# type = stream
+# url = http://radio1.example.com:8000/live
+# format = auto
+# filename_pattern = radio1_%Y%m%d_%H%M%S
+#
+# [radio_station_2]
+# type = stream
+# url = http://radio2.example.com:8000/live
+# format = auto
+# filename_pattern = radio2_%Y%m%d_%H%M%S
+#
+# [system_audio]
+# type = soundcard
+# device = Stereo Mix
+# sample_rate = 48000
+# channels = 2
+# format = flac
+# filename_pattern = system_%Y%m%d_%H%M%S
+
+
+# =============================================================================
+# SOUNDCARD TIPS (Linux / Raspberry Pi)
+# =============================================================================
+# ISR uses ALSA (arecord) for soundcard recording. arecord is pre-installed
+# on Raspberry Pi OS and most Linux distros (package: alsa-utils).
+#
+# Run: python isr.py --list-devices   (or: arecord -l) to list devices.
+#
+# EASY: Use the "monitor" keyword to capture system/loopback audio:
+# [system_audio]
+# type = soundcard
+# device = monitor
+# format = wav
+#
+# MANUAL: Specify a device by ALSA hardware ID from --list-devices:
+# [usb_mic]
+# type = soundcard
+# device = hw:1,0
+# backend = alsa
+# sample_rate = 44100
+# channels = 2
+# format = flac