docs: Complete documentation modernization

[db-tycoon-stephen]

Summary

Finish documentation modernization started in previous releases.

Motivation

From roadmap Priority 2:

• Update remaining documentation references
• Consolidate operational guides
• Remove outdated dual-repo instructions

Tasks

1. Update References

   • Remove any references to deprecated snowtower-cli repo
   • Update command examples to current format
   • Fix broken internal links

2. Consolidate Guides

   • Merge overlapping operational docs
   • Create unified troubleshooting guide
   • Update architecture diagrams

3. API Documentation

   • Document Python API for snowddl_core
   • Add docstrings to public functions
   • Generate API reference docs

4. Verify Accuracy

   • Audit all uv run commands in docs
   • Verify file paths are current
   • Test all code examples

Acceptance Criteria

• No references to deprecated repos
• All internal links resolve
• All code examples tested
• README statistics current

[db-tycoon-stephen]

Completed in PR #26 (merged to v0.3)