[codex] Fix stale PR and Linear open issue filters

[redreceipt]

Issue

• The stale PR checker skipped PRs whenever GitHub's aggregate review decision was CHANGES_REQUESTED, even when the requested-changes reviewer was still the person who needed a reminder or had been re-requested after follow-up commits.
• A Linear issue closed as Duplicate could still appear in open priority bug notifications because open queries excluded a few terminal state types instead of selecting Linear's open state types.

Solution

• Make stale PR reminders reviewer-specific for active requested-changes reviews: notify only the active change-requesting reviewer while that state is active, and fall back to all open review requests once the change request is cleared.
• Require a current open review request before sending a stale-review reminder, and use the latest request timestamp when calculating stale age.
• Query open Linear work with the comprehensive open state type allow-list: triage, backlog, unstarted, and started.

To Test

• source .venv-ci/bin/activate && python -m unittest discover -s tests -p 'test_*.py'
• source .venv-ci/bin/activate && ruff check .
• source .venv-ci/bin/activate && ruff format --check .
• source .venv-ci/bin/activate && vulture . --config pyproject.toml
• source .venv-ci/bin/activate && mypy .

Proof

• Runtime proof ran jobs.post_stale() against a local Slack-compatible webhook and showed only the active change-requesting reviewer notified.
• Runtime proof also exercised github.get_prs_waiting_for_review_by_reviewer() and live linear.issues.get_open_issues(2, "Bug"), confirming APO-8787 is absent from open priority bugs.
• Full test suite passed: 90 tests.
• Ruff, format check, vulture, and mypy passed locally.
• GitHub CI is green for ruff, mypy, unit-tests, vulture, and gunicorn-smoke.

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