docs: use uv sync to install docs dependencies in ReadTheDocs build

[jarsarasty]

• ReadTheDocs was using pip to install the docs extra, which failed to resolve sphinx_copybutton and other Sphinx
  dependencies. The fix switches to uv sync --group docs with an explicit Sphinx build command, consistent with how
  dependencies are managed in the rest of the project.
• Fix typo due to stale API reference in getting_started.rst: get_esdl_with_kpis → build_esdl_with_kpis

[Copilot]

Pull request overview

Updates documentation and Read the Docs build configuration to align docs builds with the project’s uv-based dependency workflow.

Changes:

• Fix Getting Started example to call KpiManager.build_esdl_with_kpis(...) (matches current API).
• Switch ReadTheDocs build to install docs dependencies via uv sync --group docs.
• Run Sphinx via uv run ... in the RTD build commands.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
doc/getting_started.rst	Updates an example to use the correct KpiManager method name for building an ESDL object with embedded KPIs.
.readthedocs.yaml	Replaces RTD’s python.install/extras flow with explicit uv-based dependency installation and an explicit Sphinx build command.

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