feat: needs.json merger

[AlexanderLanin]

Summary

• add a Bazel CLI to merge Sphinx-Needs needs.json inventories
• validate input structure and reject conflicting Need definitions
• write output atomically and preserve existing results on failure
• add unit and Sphinx app-level coverage, including empty inventories
• reuse public docs_bundle targets for test data instead of redundant source filegroups

Validation

• bazel test //scripts_bazel/tests:merge_needs_json_unit_tests //scripts_bazel/tests:merge_needs_json_app_tests --test_output=errors
• bazel build //scripts_bazel:merge_needs_json
• commit hooks: Ruff, BasedPyright, copyright checks

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run --lockfile_mode=error //src:license-check

Status: ⚠️ Needs Review

Click to expand output

[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.6.0) and connecting to it...
INFO: Invocation ID: 0f089d50-0099-451d-a2d5-9c57fdbbb721
Computing main repo mapping: 
Loading: 
Loading: 0 packages loaded
Loading: 0 packages loaded
Loading: 0 packages loaded
    currently loading: src
WARNING: Target pattern parsing failed.
ERROR: Skipping '//src:license-check': no such target '//src:license-check': target 'license-check' not declared in package 'src' defined by /home/runner/work/docs-as-code/docs-as-code/src/BUILD
ERROR: no such target '//src:license-check': target 'license-check' not declared in package 'src' defined by /home/runner/work/docs-as-code/docs-as-code/src/BUILD
INFO: Elapsed time: 5.490s
INFO: 0 processes.
ERROR: Build did NOT complete successfully
ERROR: Build failed. Not running target

[github-actions]

Documentation preview for this pull request is available at:
pr-733: https://eclipse-score.github.io/docs-as-code/pr-733/

[AlexanderLanin]

discussed in call @AlexanderLanin @a-zw @MaximilianSoerenPollak: drop app tests, they will be executed implicitly in bundle tests soon