ci: exercise companyscope and sentinel on Python 3.11 through 3.13

[dinakarjs]

Closes #238. Add separate GitHub Actions workflows for companyscope-incident-register and sentinel, using the existing integration workflow pattern and Python 3.11, 3.12 and 3.13. Each runs on relevant pushes/PRs, weekly, and on manual dispatch, with SHA-pinned checkout/setup-python actions and read-only contents permission.

CompanyScope installs agent-manifest and pytest and runs its existing eight tests. It produces a human review pack, not a TRACE record, so its workflow does not invent an emit step. Sentinel installs its own requirements-dev.txt and runs its seventeen tests, including TRACE Level 0 signature verification. Separate jobs preserve the integrations’ import paths and dependencies.

Validation:

• companyscope-incident-register: 8 passed on each of Python 3.11, 3.12 and 3.13.
• sentinel: 17 passed on each of Python 3.11, 3.12 and 3.13; no skips. Existing Pydantic and Starlette deprecation warnings remain.
• actionlint 1.7.12: both new workflows pass.
• git diff --check passes.

Only the two workflow files are changed. Upstream Actions runs may require approval for this first contribution.

Prepared with AI assistance; changes and test results reviewed.