feat: Add /speckit.prd command to import and sync with existing PRD

[sbhavani]

Summary

Add a command to import an existing PRD (Product Requirements Document) and list prioritized features as candidates for /speckit.specify.

I'm happy to create a PR if this would be useful.

Use Case

Many projects already have a PRD.md that defines:

• Prioritization where MoSCoW (Must/Should/Could/Won't) is common
• Feature roadmap with status

Currently there's a gap between the PRD (product-level) and /speckit.specify (feature-level). Users manually find features in their PRD, then run
/speckit.specify separately with no linkage.

Proposed Command

/speckit.prd <path>

Import a PRD and list TODO items by priority:

/speckit.prd docs/PRD.md

Then prompt: "Which feature would you like to specify?" and feed selection into /speckit.specify.

PRD Format Support

Should parse common patterns:

<!-- MoSCoW table -->                                                                                                                                           
| Feature | Status | Description |                                                                                                                              
|---------|--------|-------------|                                                                                                                              
| CSV Export | TODO | Export results as CSV |                                                                                                                   
                                                                                                                                                                
<!-- Checkbox list -->                                                                                                                                          
- [ ] CSV export for evaluation results                                                                                                                         
- [x] Docker deployment                                                                                                                                         
                                                                                                                                                                
<!-- Roadmap section -->                                                                                                                                        
### Should Have                                                                                                                                                 
1. **CSV Export** - TODO - Export results as CSV                                                                                                                
                                                                                                                                                                

[emi-dm]

Hi @sbhavani ! It is a good idea because there is an obvious gap between the requirements that the model understands based on the context and a clear PRD. Maybe It could be interesting if you also introduce tags for priority level!

[sbhavani]

I've been working on this workflow in (speckit-agents)

The PM Agent reads your docs/PRD.md, checks git history to see what's already implemented, then suggests the highest priority feature that hasn't been built yet. It feeds straight into /speckit.specify.

I'd love to get some feedback on the PRD format (full example):

  ### P0: Core Workflow
  - [P0-US1] PM Agent reads PRD and suggests features