script-mode task execution — database-backed tasks with direct script runner

Tasks now live in the database (mode: script or agentic). Script-mode tasks
bypass the agent entirely — the implementation is materialized to a temp file
and executed directly, with stdout/stderr streamed to the UI via WebSocket.

Includes convert-to-mp3 as the first native script task.

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

seed/tasks/convert-to-mp3/TASK.md

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+---
+name: Convert To MP3
+description: Convert audio files to MP3 320kbps, preserving metadata.
+version: 1
+mode: script
+language: bash
+triggers:
+  - type: file
+    extensions:
+      - flac
+      - wav
+      - ogg
+      - wma
+      - aac
+      - m4a
+      - opus
+      - aiff
+      - aif
+      - ape
+      - wv
+      - alac
+      - dsf
+      - dff
+  - type: directory
+inputs:
+  file_path:
+    type: string
+    description: Path to an audio file or directory to convert.
+args: [file_path]
+---
+
+# Convert To MP3
+
+Convert audio files to MP3 320kbps using ffmpeg, preserving metadata.
+Supports single file conversion and batch directory conversion.

seed/tasks/convert-to-mp3/run.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+# Accepts path as $1 or $INPUT_FILE_PATH
+TARGET="${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
+
+convert_file() {
+  local input="$1"
+  local ext="${input##*.}"
+  local dir
+  dir="$(dirname "$input")"
+  local base
+  base="$(basename "$input" ".$ext")"
+  local output="$dir/$base.mp3"
+
+  if [[ "${ext,,}" == "mp3" ]]; then
+    echo "Skipping (already MP3): $input"
+    return 0
+  fi
+
+  if [[ -f "$output" ]]; then
+    echo "Skipping (output exists): $output"
+    return 0
+  fi
+
+  echo "Converting: $input → $output"
+  ffmpeg -i "$input" -codec:a libmp3lame -b:a 320k -map_metadata 0 -id3v2_version 3 -y "$output" 2>/dev/null
+
+  if [[ $? -eq 0 ]]; then
+    echo "  ✓ Done"
+  else
+    echo "  ✗ Failed" >&2
+    return 1
+  fi
+}
+
+AUDIO_EXTS="flac|wav|ogg|wma|aac|m4a|opus|aiff|aif|ape|wv|alac|dsf|dff"
+converted=0
+failed=0
+
+if [[ -f "$TARGET" ]]; then
+  if convert_file "$TARGET"; then
+    converted=$((converted + 1))
+  else
+    failed=$((failed + 1))
+  fi
+elif [[ -d "$TARGET" ]]; then
+  while IFS= read -r -d '' file; do
+    if convert_file "$file"; then
+      converted=$((converted + 1))
+    else
+      failed=$((failed + 1))
+    fi
+  done < <(find "$TARGET" -type f -regextype posix-extended -iregex ".*\.($AUDIO_EXTS)" -print0 | sort -z)
+
+  if [[ $converted -eq 0 && $failed -eq 0 ]]; then
+    echo "No audio files found in: $TARGET"
+    exit 0
+  fi
+else
+  echo "Error: Not a file or directory: $TARGET" >&2
+  exit 1
+fi
+
+echo ""
+echo "Summary: $converted converted, $failed failed"