add pipeline task system, agentic music tasks, copy buttons, and pi-bridge cleanup

- Pipeline mode: new task mode that chains agentic tasks sequentially with
  foreach/subdirectory iteration and skip_if conditions
- Pipeline executor backend (WebSocket at /api/tasks/pipeline/ws) with
  support for both Pi and Claude Code models
- Frontend PipelineRunner component with step progress, streaming output,
  and aggregate cost tracking
- New agentic tasks: prepare-discography, fetch-album-info, build-discography
  (pipeline combining both)
- Seed parser extended to handle pipeline steps in frontmatter config
- CopyButton component added to assistant bubbles, error bubbles, and
  tool input/output sections
- Removed obsolete SearXNG/Apify/browser relay code from pi-bridge

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

src/servers/api/tasks/tasks.ts

@@ -47,6 +47,7 @@ tasksRouter.get('/:name', async (ctx) => {
     inputs: task.inputs,
     args: task.args,
     trigger: task.trigger,
+    config: task.config,
     version: task.version,
     userId: task.userId,
   });