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/fix-sd.nix

@@ -0,0 +1,34 @@
+# Recover files from a corrupted exFAT SD card
+{
+  writers,
+  exfatprogs,
+  util-linux,
+  coreutils,
+  findutils,
+  gnused,
+}:
+writers.writeDashBin "fix-sd" ''
+  set -efu
+
+  drive="''${1:?Usage: fix-sd /dev/sdX [output-dir]}"
+  output_dir="''${2:-$(${coreutils}/bin/mktemp -d "''${TMPDIR:-/tmp}/fix-sd-XXXXXX")}"
+  mountpoint="$(${coreutils}/bin/mktemp -d "''${TMPDIR:-/tmp}/fix-sd-mount-XXXXXX")"
+
+  trap clean EXIT
+  clean() {
+    ${util-linux}/bin/umount "$mountpoint" 2>/dev/null || true
+    ${coreutils}/bin/rmdir "$mountpoint" 2>/dev/null || true
+  }
+
+  filenames="$(${exfatprogs}/bin/fsck.exfat "$drive" 2>&1 | ${gnused}/bin/sed -nE "s/.* file '(.*?)' is not allocated.*/\1/p")"
+  ${coreutils}/bin/mkdir -p "$mountpoint" "$output_dir"
+  ${util-linux}/bin/mount "$drive" "$mountpoint"
+
+  echo "$filenames" | while read -r filename; do
+    [ -n "$filename" ] || continue
+    ${findutils}/bin/find "$mountpoint" -type f -name "$filename" -exec ${coreutils}/bin/cp {} "$output_dir" \;
+  done
+
+  echo "Recovered files saved to $output_dir"
+  ${exfatprogs}/bin/fsck.exfat "$drive"
+''