fix: respect Bazel package boundaries in mounted docs

[AlexanderLanin]

Summary

Make runtime Sphinx discovery follow the same direct source ownership that Bazel applies to docs_bundle(source_dir = ...).

The mounts manifest now records an anchored include allowlist for each bundle and a separate primary_source record for the project source tree. score_mounts passes the allowlist to sphinx-mounts for child bundles and excludes unowned RST/Markdown files from the primary Sphinx source tree.

This prevents a parent source directory from recursively exposing documents below nested Bazel packages. Those documents are then supplied exactly once by their declared child bundle.

Regression coverage

The subdirectory_bundle scenario now places the child bundle under the producer's docs/ directory, with its own BUILD file. It verifies producer and consumer needs_json, rendered docs, strict docs checks, and link checks. Resolver coverage verifies the new manifest fields; the existing nested-bundles scenario remains unchanged and passes.

Fixes #781

[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: 59fabd6b-a5ec-402c-9fc8-ae7807cede34
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: 5.656s
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-782: https://eclipse-score.github.io/docs-as-code/pr-782/

[AlexanderLanin]

closing in favor of #784