generalize convert-to-mp3 into convert-audio with selectable target format

- rename task to convert-audio, support mp3/flac/wav/ogg/aac/opus targets
- add options input type with selectable pill buttons in UI
- extend seed script parser to handle YAML list properties (options)

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

seed/tasks/convert-audio/TASK.md

@@ -0,0 +1,51 @@
+---
+name: Convert Audio
+description: Convert audio files between formats, preserving metadata.
+version: 1
+mode: script
+language: bash
+triggers:
+  - type: file
+    extensions:
+      - mp3
+      - 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.
+  target_format:
+    type: string
+    description: Target format
+    default: mp3
+    options:
+      - mp3
+      - flac
+      - wav
+      - ogg
+      - aac
+      - opus
+  delete_source:
+    type: boolean
+    description: Delete source files after successful conversion.
+    default: false
+args: [file_path]
+---
+
+# Convert Audio
+
+Convert audio files between formats using ffmpeg, preserving metadata.
+Supports single file conversion and batch directory conversion.