feat: interactive architecture generation (specsmith architect)

[tbitcs]

Summary

Add a specsmith architect command that generates or enriches architecture
documentation by scanning the project and conducting an interactive interview.

Proposed Workflow

1. Scan project structure, modules, languages, dependencies, entry points
2. Scan git history for architecture-relevant commits (refactors, new modules)
3. Scan existing docs (REQUIREMENTS.md, AGENTS.md) for architectural references
4. Present a draft architecture to the user
5. Run an interactive interview asking about:
   • Major components and their responsibilities
   • Data flow between components
   • External interfaces and dependencies
   • Deployment model
   • Platform-specific considerations
6. Generate or update docs/architecture.md with the combined information
7. Optionally generate a component diagram (text-based, Mermaid or ASCII)

Integration Points

• specsmith import --guided already does basic component prompts - this would
  replace that with the richer version
• specsmith audit would recommend running architect when architecture.md
  is missing or stale
• specsmith export would include architecture summary in compliance reports

Design Considerations

• Must work offline (no LLM required) - the interview is deterministic prompts
• AI agents can be used AFTER to enrich the generated scaffold
• Should detect and reference existing architecture docs in non-standard locations

[tbitcs]

Implemented in 5b7ad9c