Gate long-running examples in documentation CI

[Copilot]

The documentation workflow was failing because routine docs builds on main automatically executed the long-running Literate examples, and one_degree_simulation.jl was crashing that path. This change narrows when full-example docs builds run so normal documentation builds stay on the stable subset.

• Workflow gating

  • Add a workflow_dispatch boolean input, build_all_examples
  • Set NUMERICAL_EARTH_BUILD_ALL_EXAMPLES=true only when:
    • the workflow is manually dispatched with build_all_examples: true, or
    • a PR carries the existing build all examples label
  • Stop enabling full-example docs builds implicitly on every main/tag push

• Docs behavior alignment

  • Update the docs/make.jl comment to match the new contract for long-running examples

if [[ "${GITHUB_EVENT_NAME}" == "workflow_dispatch" && "${BUILD_ALL_EXAMPLES_INPUT}" == "true" ]] || \
   [[ "${GITHUB_EVENT_NAME}" == "pull_request" && "${HAS_BUILD_ALL_LABEL}" == "true" ]]; then
    NUMERICAL_EARTH_BUILD_ALL_EXAMPLES=true
else
    NUMERICAL_EARTH_BUILD_ALL_EXAMPLES=false
fi

[simone-silvestri]

I think this is incorrect, we need to switch examples we want to run on the PRs to false, not change the pipeline

[xkykai]

Yeah I think this solution is wrong, but we should probably fix docs build for merges into main. I was just trying to check if the new example builds correctly.