refactor: transport external needs labels explicitly

[AlexanderLanin]

Motivation

External Needs enter the documentation build as Bazel labels. The sandboxed needs_json action did not pass those labels through the same path as regular documentation builds, and the old docs_sources/sphinx-collections path mixed documentation mounts with Needs inventory handling.

The goal is one clear architecture:

• Bazel declares the inputs.
• The CLI passes the labels and runfiles root to Sphinx.
• score_metamodel handles external Needs inventories.
• score_mounts handles documentation source mounts.
• All build modes use the same path rules.

Sphinx accepts --define values as text, so the CLI sends the labels as JSON. This is only a transport format; the labels are parsed in score_metamodel, which resolves the corresponding Needs files.

Changes

• Pass explicitly declared external Needs labels from docs() into the sandboxed Needs action through EXTERNAL_NEEDS_LABELS.
• Combine the relevant Bazel label inputs in the documentation CLI and pass them to Sphinx with the runfiles root.
• Centralize label parsing and runfiles path rules for needs_json and needs_json_file.
• Register resolved files as Sphinx-Needs external inventory entries.
• Remove the obsolete config.collections path and sphinx-collections dependency.
• Keep documentation source mounts in mounts_manifest, consumed by score_mounts.
• Update the affected tests.

[github-actions]

Documentation preview for this pull request is available at:
pr-840: https://eclipse-score.github.io/docs-as-code/pr-840/

[Copilot]

🟢 Approval recommended

The transport and resolution paths are consistent, obsolete integration is removed, and focused tests cover the new behavior.

Review details

• Files reviewed: 14/14 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[MaximilianSoerenPollak]

Talked about in a call and all questions answered.

Looks good