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>

seed/templates/SCRIPTS.md

@@ -20,6 +20,17 @@ All task inputs defined in the TASK.md frontmatter are available to the script i
 
 Inputs provided by context (e.g. `file_path` from the file browser) are auto-filled and hidden from the form.
 
+### Autofill
+
+Inputs can declare `autofill` to pre-fill from the trigger context. Available context values:
+
+| Value | Source |
+|-------|--------|
+| `entry_name` | Name of the file or directory that triggered the task |
+| `entry_path` | Full path of the file or directory |
+
+Autofilled inputs are visible and editable (unlike `file_path` which is hidden).
+
 ## Templates
 
 ### 1. File Processor
@@ -180,6 +191,7 @@ inputs:
     type: string             # string, number, boolean
     description: What this input is
     default: value           # optional — default value
+    autofill: entry_name     # optional — pre-fill from context (entry_name or entry_path)
     options:                 # optional — renders as selectable pills in UI
       - option1
       - option2