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/json2csv.nix

@@ -0,0 +1,32 @@
+# Convert JSON array of objects to CSV
+{
+  writers,
+  python3,
+}:
+writers.writePython3Bin "json2csv" {
+  flakeIgnore = [ "E501" ];
+} ''
+  import csv
+  import json
+  import sys
+
+  if __name__ == "__main__":
+      json_list = json.load(sys.stdin)
+      if not isinstance(json_list, list):
+          print("JSON object is not a list.", file=sys.stderr)
+          sys.exit(1)
+      if len(json_list) == 0:
+          print("JSON list is empty.", file=sys.stderr)
+          sys.exit(1)
+      keys = set()
+      for element in json_list:
+          if isinstance(element, dict):
+              keys |= element.keys()
+          else:
+              print("Non-dict element:", element, file=sys.stderr)
+              sys.exit(1)
+      writer = csv.DictWriter(sys.stdout, fieldnames=list(keys))
+      writer.writeheader()
+      for element in json_list:
+          writer.writerow(element)
+''