Add optional redesigned React based web interface

[calvind80]

Summary

Adds an optional modern React interface while preserving the existing Predbat interface as the default.

Setting web_ui: modern in apps.yaml serves the bundled modern interface. If the option is omitted or set to legacy, Predbat continues to use the existing interface.

The new interface includes:

• Responsive dashboard and energy overview
• Plan timeline, table, history and debug views
• Battery, power, cost, rates, solar, savings, degradation, marginal-cost and CO₂ charts
• Apps configuration editor with schema help and Home Assistant entity autocomplete
• Tariff helper with reviewable configuration suggestions
• Entities, logs, compare, annual, discovery, cards, internals and documentation pages
• Home Assistant ingress navigation and mobile layouts
• Optional weather effects and configurable Overview integrations
• PredHeat configuration reuse for weather and heat-pump data

Compatibility

• The legacy interface remains the default.
• Users do not need Node.js or Vite. The compiled interface is included in apps/predbat/frontend.zip.
• Existing apps.yaml configurations remain supported.
• Modern-only entities and settings are optional.
• Frontend source remains available under frontend/.

Validation

• 49 frontend tests passed
• Frontend lint completed with no errors
• TypeScript and Vite production build passed
• Modern frontend bundle generated successfully
• Focused power-flow and Overview backend tests passed
• Full Predbat suite: 334 tests passed
• All pre-commit checks passed
• Tested through Home Assistant ingress on desktop and mobile

[raldred]

Thanks for the PR, Can you share screenshots of the various features of the proposed dashboards?