feat: support agentic sync without architecture.json (#538)

[prompt-driven-github]

Summary

Enable agentic sync (pdd sync <issue-url>) to work on projects that do not have an architecture.json file by scanning the prompts/ directory for module prompt files and building a module catalog for the LLM to select from.

Closes #538

Changes Made

Prompts Modified

• pdd/prompts/agentic_sync_identify_modules_LLM.prompt — Added conditional logic so the LLM uses architecture.json when available, but falls back to a {module_catalog} (built from prompts/ directory scan) when it is not. Added <pdd-interface> metadata. Made dependency validation conditional (bypass when no architecture.json).

Code Modified

• pdd/agentic_sync.py — Added logic to scan prompts/ directory for *_*.prompt files (excluding *_LLM.prompt), build a module catalog string, and pass it to the prompt template via the new {module_catalog} placeholder.

Documentation Updated

• README.md — Added pdd sync to the command listing and documented agentic mode behavior with/without architecture.json
• docs/TUTORIALS.md — Added "Method 5: Syncing Modules from a GitHub Issue" tutorial section
• docs/faq.md — Added FAQ entry about using pdd sync without architecture.json

Review Checklist

• Prompt syntax is valid (placeholders, markers, output format)
• PDD conventions followed (<pdd-reason>, <pdd-interface> tags)
• Existing behavior preserved when architecture.json is present
• Module catalog correctly excludes *_LLM.prompt files
• Documentation is accurate and up to date

Next Steps After Merge

1. Regenerate code from modified prompts in dependency order:

   ./sync_order.sh

   Or manually: No modules to sync (prompt-only change)
2. Run tests to verify functionality
3. Deploy if applicable

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Created by pdd change workflow