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/chunk-pdf.nix

@@ -0,0 +1,30 @@
+# Split a PDF into chunks of N pages
+{
+  writers,
+  pdftk,
+  gnugrep,
+  coreutils,
+}:
+writers.writeDashBin "chunk-pdf" ''
+  set -efu
+
+  INPUT_FILE="''${2:?Pass the PDF path as second argument.}"
+  PAGES_PER_REPORT="''${1:?Pass the chunk size as first argument.}"
+
+  if [ ! -f "$INPUT_FILE" ]; then
+    echo >&2 "File $INPUT_FILE does not exist."
+    exit 1
+  fi
+
+  TOTAL_PAGES="$(${pdftk}/bin/pdftk "$INPUT_FILE" dump_data | ${gnugrep}/bin/grep NumberOfPages | ${coreutils}/bin/cut -f2 -d' ')"
+
+  RUNS=$((TOTAL_PAGES/PAGES_PER_REPORT))
+
+  for run in $(${coreutils}/bin/seq 0 "$((RUNS-1))"); do
+    start_page=$((run*PAGES_PER_REPORT+1))
+    end_page=$(((run+1)*PAGES_PER_REPORT))
+    output_file="chunk_$((run+1)).pdf"
+    echo "splitting $INPUT_FILE from $start_page to $end_page into $output_file"
+    ${pdftk}/bin/pdftk "$INPUT_FILE" cat "$start_page-$end_page" output "$output_file"
+  done
+''