package .bin/ scripts as proper nix packages, delete .bin/

Packaged 14 scripts from .bin/ into packages/ with proper dependency
declarations (writers.writeDashBin/writeBashBin/writePython3Bin):
- 256color → two56color (terminal color chart)
- avesta.sed → avesta (Avestan transliteration)
- bvg.sh → bvg (Berlin transit disruptions)
- unicode → charinfo (Unicode character info)
- chunk-pdf → chunk-pdf (split PDFs by page count)
- csv2json → csv2json (CSV to JSON converter)
- fix-sd.sh → fix-sd (exFAT SD card recovery, improved output handling)
- json2csv → json2csv (JSON to CSV converter)
- mp3player-write → mp3player-write (audio conversion for MP3 players)
- mushakkil.sh → mushakkil (Arabic diacritization)
- nix-haddock-index → nix-haddock-index (GHC Haddock index generator)
- pdf-ocr.sh → pdf-ocr (OCR PDFs via tesseract)
- prospekte.sh → prospekte (German supermarket flyer browser)
- readme → readme (GitHub README as man page)

All added to overlay and packages output. .bin/ directory removed.

packages/mp3player-write.nix

@@ -0,0 +1,89 @@
+# Convert and transfer audio files to an MP3 player
+{
+  writers,
+  ffmpeg,
+  coreutils,
+  gnugrep,
+  bash,
+}:
+writers.writeBashBin "mp3player-write" ''
+  set -e
+
+  SPEED=1.0
+
+  while getopts ":s:" opt; do
+    case $opt in
+      s) SPEED=$OPTARG ;;
+      \?) echo "Invalid option: -$OPTARG" >&2; exit 1 ;;
+      :) echo "Option -$OPTARG requires a value." >&2; exit 1 ;;
+    esac
+  done
+  shift $((OPTIND -1))
+
+  if [ "$#" -lt 2 ]; then
+    echo "Usage: mp3player-write [-s speed] MOUNT_POINT FILE1 [FILE2 ...]"
+    exit 1
+  fi
+
+  MOUNT_POINT=$1
+  shift
+  FILES=("$@")
+
+  if [ ! -d "$MOUNT_POINT" ]; then
+    echo "Error: Mount point '$MOUNT_POINT' does not exist."
+    exit 1
+  fi
+
+  TOTAL_SIZE=0
+  for f in "''${FILES[@]}"; do
+    if [ ! -f "$f" ]; then
+      echo "Warning: File '$f' does not exist, skipping."
+      continue
+    fi
+    FILE_SIZE=$(${coreutils}/bin/stat --printf="%s" "$f")
+    TOTAL_SIZE=$((TOTAL_SIZE + FILE_SIZE / 2))
+  done
+
+  AVAILABLE=$(${coreutils}/bin/df --output=avail "$MOUNT_POINT" | ${coreutils}/bin/tail -n 1)
+  AVAILABLE=$((AVAILABLE * 1024))
+
+  if [ "$TOTAL_SIZE" -gt "$AVAILABLE" ]; then
+    echo "Error: Not enough space. Required: $TOTAL_SIZE bytes, Available: $AVAILABLE bytes"
+    exit 1
+  fi
+
+  echo "Enough space available. Starting conversion..."
+
+  sanitize_filename() {
+    local name
+    name=$(${coreutils}/bin/basename "$1")
+    name=''${name%.*}
+    name=$(echo "$name" | ${coreutils}/bin/tr ' ' '_' | ${coreutils}/bin/tr -cd '[:alnum:]_-')
+    echo "''${name:0:50}"
+  }
+
+  for f in "''${FILES[@]}"; do
+    [ -f "$f" ] || continue
+
+    existing_prefixes=$(${coreutils}/bin/ls "$MOUNT_POINT" | ${gnugrep}/bin/grep -E '^[0-9].*\.mp3$' | ${coreutils}/bin/sed -E 's/^([0-9]).*/\1/' | ${coreutils}/bin/sort -n | ${coreutils}/bin/uniq)
+    for i in {0..9}; do
+      if ! echo "$existing_prefixes" | ${gnugrep}/bin/grep -q "^$i$"; then
+        PREFIX=$i
+        break
+      fi
+    done
+
+    BASENAME=$(sanitize_filename "$f")
+    OUT_PATTERN="$MOUNT_POINT/''${PREFIX}_%03d_''${BASENAME}.mp3"
+
+    echo "Converting '$f' to '$OUT_PATTERN' at speed $SPEED..."
+
+    ${ffmpeg}/bin/ffmpeg -nostdin -i "$f" \
+      -filter:a "atempo=$SPEED" \
+      -ar 22050 -ac 1 -c:a libmp3lame -b:a 32k \
+      -f segment -segment_time 300 \
+      "$OUT_PATTERN"
+  done
+
+  echo "All files processed successfully."
+''