add script task templates and refactor convert-to-mp3 to use template pattern

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

seed/templates/file-processor.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# ── File Processor Template ──
+# Handles: input resolution, validation, file discovery, iteration, summary.
+# The task only needs to define: EXTENSIONS and process_file().
+#
+# Slots to fill before this template:
+#   EXTENSIONS="flac|wav|ogg"          — pipe-separated list of file extensions to match
+#   process_file() { ... }            — receives $1 (input path), returns 0 on success
+
+# ── Input resolution ──
+TARGET="${1:-${INPUT_FILE_PATH:-}}"
+
+if [[ -z "$TARGET" ]]; then
+  echo "Error: No file or directory path provided" >&2
+  exit 1
+fi
+
+if [[ ! -e "$TARGET" ]]; then
+  echo "Error: Path does not exist: $TARGET" >&2
+  exit 1
+fi
+
+# ── Execution ──
+converted=0
+failed=0
+
+if [[ -f "$TARGET" ]]; then
+  if process_file "$TARGET"; then
+    converted=$((converted + 1))
+  else
+    failed=$((failed + 1))
+  fi
+elif [[ -d "$TARGET" ]]; then
+  while IFS= read -r -d '' file; do
+    if process_file "$file"; then
+      converted=$((converted + 1))
+    else
+      failed=$((failed + 1))
+    fi
+  done < <(find "$TARGET" -type f -regextype posix-extended -iregex ".*\.($EXTENSIONS)" -print0 | sort -z)
+
+  if [[ $converted -eq 0 && $failed -eq 0 ]]; then
+    echo "No matching files found in: $TARGET"
+    exit 0
+  fi
+else
+  echo "Error: Not a file or directory: $TARGET" >&2
+  exit 1
+fi
+
+echo ""
+echo "Summary: $converted processed, $failed failed"