Add Civ Lite city management

[YfengJ]

Summary

• add a tested Civ Lite city economy model for worked tiles, building effects, growth, happiness, amenities, and production spending
• add a compact City Management sidebar panel with city stats, worked tile summary, yields, and building actions
• route per-turn city yields through the model, keep player production banked for buildings, and preserve bot auto-recruitment for prototype pressure
• fix sidebar section shrinking so city management controls cannot overlap the action buttons

Closes #19

Validation

• node --test demo/civ-lite/city-model.test.mjs
• node --check demo/civ-lite/city-model.js && node --check demo/civ-lite/game.js && node --check demo/civ-lite/sprites.js
• git diff --check
• Playwright/Chrome smoke against local http.server: city panel renders Athens, End Turn is not intercepted by the city panel, production banks over turns, Granary becomes buildable and registers as built, and canvas renders non-empty pixels

[YfengJ]

CI follow-up:

• SonarCloud Code Analysis now passes on latest head 5b8ec61.
• The remaining red check is the existing Godot Web export preset failure:
  Cannot export project with preset "Web" due to configuration errors

This PR only touches the Civ Lite browser prototype files under demo/civ-lite/, so I do not see a contributor-side code failure in the city management change. I will keep watching for maintainer feedback or any concrete follow-up request.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud