Update documentation

[jravani]

Update project documentation

Summary

As part of the upcoming beta release, the project documentation needs a full update to reflect the current software version and the new framework.

We are moving from Read the Docs to MkDocs, and the site should be hosted via GitHub Pages.

Scope

• Refresh all documentation so it matches the current behaviour and CLI/API of City2TABULA
• Document the pipeline/modules in enough detail that a new user can install, configure, run, and interpret outputs without guesswork
• Add diagrams where they improve understanding (architecture, workflow, data flow, DB schema/relations, etc.)

Documentation platform changes

• Replace Read the Docs setup with MkDocs
• Configure deployment to GitHub Pages (CI-based publishing preferred)

Content requirements

• Installation and prerequisites (incl. PostGIS, dataset expectations, any required tooling)
• Configuration reference (env/config keys, defaults, examples)
• Usage guide (CLI commands, common workflows, expected outputs)
• Pipeline stages/modules explained (what each stage does, inputs/outputs, assumptions, failure modes)
• Data formats supported (CityGML/CityJSON, LoD expectations) and any limitations
• Examples / quickstart walkthrough
• Troubleshooting section (common errors and fixes)

Include other documents

• CODE_OF_CONDUCT.md
• CONTRIBUTING.md

Acceptance criteria

• MkDocs site builds with no warnings in strict mode
• Site is published to GitHub Pages
• All pages reflect the current beta version behaviour (commands, flags, outputs)
• Key workflows are documented end-to-end (install → configure → run → results)
• Diagrams included for architecture/workflow and referenced from the relevant pages
• CODE_OF_CONDUCT.md and CONTRIBUTING.md are present and linked from the docs/README