Add source bundle upward Needs exports

[AlexanderLanin]

Why this matters

Every source-bearing docs_bundle now produces a reusable Needs JSON export. This makes each bundle independently consumable for traceability and allows a documentation hierarchy to pass its Needs upward from bundle to bundle.

For a bundle without ancestors, the upward export is its own Needs JSON. For a bundle with ancestors, the upward export contains the bundle's own Needs plus the complete merged Needs of its ancestors.

Technical design

• add upward_bundles as an explicit documentation-hierarchy dependency
• build *_needs_local from a bundle's own sources while ancestor exports are available as external resolution context
• provide *_needs_upward as the merged, reusable export for the next bundle in the hierarchy
• support bundle upward targets in the external Needs runfiles resolver
• document the Bazel data flow, ownership rules, and current data-only limitation

Scope

Needs declared in generated bundle data are intentionally not included yet; this PR prepares source-bearing bundles. Data-only bundles do not create Needs targets, while source-less hierarchy groups can forward already-generated upward exports.

[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: 8437cb87-46fc-4e07-8aee-1fbf444e9ff0
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: 5.694s
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-772: https://eclipse-score.github.io/docs-as-code/pr-772/