Obia release prep

[iosefa]

Summary

This PR prepares OBIA for a cleaner release by tightening the package surface, rewriting the documentation, adding optional point-cloud feature support, and aligning release infrastructure with the Coregix workflow.

Changes

• Reworked README and MkDocs documentation around the core OBIA workflow: segmentation, feature
  extraction, labelling, classification, point-cloud enrichment, and large-raster usage.
• Added project badges and configured docs for https://obia.sefa.ai.
• Removed stale docs pages, the poor example notebook, and unrelated seed/cost-surface utilities.
• Added optional obia.pointcloud support for joining point-cloud height, intensity, and density
  metrics to segment objects.
• Added point-cloud tests and API documentation.
• Marked obia.detection as experimental in docs and navigation.
• Added pip-first installation docs, point-cloud install notes with conda-forge PDAL, Docker usage,
  and developer setup.
• Added Docker support with PDAL, Python PDAL bindings, and pyforestscan.
• Reworked GitHub Actions to match Coregix:
  • tests workflow
  • docs deploy workflow
  • PyPI publish workflow
  • Docker publish workflow

Validation

• python -m pytest -q
• mkdocs build --strict
• python -m build
• git diff --check