feat: Add interactive pre-flight checklists for ccw-loop and workflow-plan, including validation and task transformation steps

- Implemented `prep-loop.md` for ccw-loop, detailing source discovery, validation, task transformation, and auto-loop configuration.
- Created `prep-plan.md` for workflow planning, covering environment checks, task quality assessment, execution preferences, and final confirmation.
- Defined schemas and integration points for `prep-package.json` in both ccw-loop and workflow-plan skills, ensuring proper validation and task handling.
- Added error handling mechanisms for various scenarios during the preparation phases.

.codex/skills/ccw-loop/SKILL.md

@@ -57,6 +57,20 @@ Stateless iterative development loop using Codex single-agent deep interaction p
 | --loop-id | One of TASK or --loop-id | Existing loop ID to continue |
 | --auto | No | Auto-cycle mode (develop → debug → validate → complete) |
 
+## Prep Package Integration
+
+When `prep-package.json` exists at `{projectRoot}/.workflow/.loop/prep-package.json`, Phase 1 consumes it to:
+- Load pre-built task list from `prep-tasks.jsonl` instead of generating tasks from scratch
+- Apply auto-loop config (max_iterations, timeout)
+- Preserve source provenance and convergence criteria from upstream planning/analysis skills
+
+Prep packages are generated by the interactive prompt `/prompts:prep-loop`, which accepts JSONL from:
+- `collaborative-plan-with-file` (tasks.jsonl)
+- `analyze-with-file` (tasks.jsonl)
+- `brainstorm-to-cycle` (cycle-task.md → converted to task format)
+
+See [phases/00-prep-checklist.md](phases/00-prep-checklist.md) for schema and validation rules.
+
 ## Execution Modes
 
 ### Mode 1: Interactive
@@ -101,6 +115,7 @@ Phase 2: Orchestration Loop
 
 | Phase | Document | Purpose |
 |-------|----------|---------|
+| 0 | [phases/00-prep-checklist.md](phases/00-prep-checklist.md) | Prep package schema and validation rules |
 | 1 | [phases/01-session-init.md](phases/01-session-init.md) | Argument parsing, state creation/resume, directory init |
 | 2 | [phases/02-orchestration-loop.md](phases/02-orchestration-loop.md) | Agent spawn, main loop, result parsing, send_input dispatch |