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/pdf-ocr.nix

@@ -0,0 +1,29 @@
+# OCR a PDF file to text using tesseract
+{
+  writers,
+  poppler_utils,
+  tesseract,
+  coreutils,
+}:
+writers.writeDashBin "pdf-ocr" ''
+  set -efu
+
+  pdf_path="$(${coreutils}/bin/realpath "$1")"
+
+  [ -f "$pdf_path" ] || {
+    echo "Usage: pdf-ocr FILE.pdf" >&2
+    exit 1
+  }
+
+  tmpdir="$(${coreutils}/bin/mktemp -d)"
+  trap 'rm -rf $tmpdir' EXIT
+
+  cd "$tmpdir"
+
+  ${poppler_utils}/bin/pdftoppm -png "$pdf_path" pdf-ocr
+  for png in pdf-ocr*.png; do
+    ${tesseract}/bin/tesseract "$png" "$png.txt" 2>/dev/null
+  done
+
+  cat pdf-ocr-*.txt
+''