feat: Add weekly-report.sh scoped to core repos

[rubambiza]

Summary

Adds scripts/weekly-report.sh, a thin wrapper that scopes the weekly org
report to the curated core-repo allowlist instead of discovering every repo
in the org.

The wrapper resolves the org identity and the core-repo list through the
shared library (load_org_profile + get_core_repos), then invokes the
Python report generator with --repos set to exactly those repos. When the
generator is called without --repos (the previous default), org-wide
discovery is unchanged, so this is additive.

Changes

• scripts/weekly-report.sh — wrapper: resolves org + core allowlist, builds
  report.py --org <org> --repos <core repos> [--since/--until/--output/--json-output],
  fails loud when the allowlist is empty or the generator is missing.
  Supports --profile and --org overrides.
• tests/test-weekly-report.sh — hermetic test (fixture allowlist via
  CORE_REPOS_FILE, stub generator via REPORT_PY): asserts arg-building,
  --since/--until pass-through, and fail-loud on a missing generator. No
  network or real config touched.
• .github/workflows/tests.yml — wires the new test into the suite runner.

The companion --repos support in the generator lives in
rossoctl/agent-skills (separate PR).

Fixes #57

Assisted-By: Claude Code

[clawgenti]

Adds scripts/weekly-report.sh, a thin wrapper that resolves the org identity and core-repo allowlist via the shared library, then invokes report.py --repos scoped to exactly those repos — plus a hermetic test covering arg-building, date-range pass-through, and fail-loud on a missing generator.

All checks pass. Ready for human review.

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Reviewed by clawgenti using the github-pr-review skill