docs: add manual StockFit review guide

[FLABDUL]

Summary

• add Windows-focused developer setup and architecture overview to the main README
• expand the StockFit learning guide into a structured code-level review with diagrams, breakpoints and exercises
• add reusable VS Code launch configurations for the offline demo, audit and tests
• document the existing native-Windows Sphinx filename collision and the WSL/Linux CI workaround

Verification

• 424 tests passed, 3 skipped, 12 deselected
• 164 focused StockFit tests passed
• Ruff formatting and lint checks passed
• Pyrefly reported 0 errors
• offline demo and audit produced the expected derived outputs
• VS Code JSON and local Markdown links validated

Known limitation

Native Windows Sphinx builds still fail because generated Cash and cash API stub filenames collide on a case-insensitive filesystem. This pre-existing issue is now documented; the documentation gates should run in WSL or Linux CI.