Refactor UI into feature modules (templates, generation/history split, server formatting helpers)

[danohn]

Summary

This PR continues the modularization plan with no intended behavior changes.

Included in this PR

1. Split template modals into dedicated components:

• src/features/templates/TemplateDetailsModal.jsx
• src/features/templates/TemplatePrerequisitesModal.jsx
• src/features/templates/TemplateModals.jsx now composes both

2. Extracted server formatting utilities from settings UI into:

• src/lib/serverFormatting.js

3. Added unit tests for extracted server formatting logic:

• src/lib/serverFormatting.test.js

4. Split HomePage internals into feature components:

• src/features/generation/GenerationPanel.jsx
• src/features/history/RecentJobsPanel.jsx
• src/features/home/HomePage.jsx now composes these

5. Added architecture notes and updated structure docs:

• README.md

Not included

• Integration tests (intentionally parked for later)

Validation

• npm test passes (18 tests)
• npm run build passes

Notes

• App.jsx remains orchestration-focused at ~584 lines.
• Refactor is intended to preserve existing runtime behavior while improving maintainability and separation of concerns.