ref(seer): Include project slug-id map for repo-project fetch

[kddubey]

re-use get_repo_and_projects

need this map for bug pred to pass as part of user_org_context in https://github.com/getsentry/seer/pull/5592/

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

Backend Test Failures

Failures on 24ed07a in this run:

tests/sentry/seer/fetch_issues/test_utils.py::TestGetRepoAndProjects::test_get_repo_and_projects_no_configs — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/seer/fetch_issues/test_utils.py:79: in test_get_repo_and_projects_no_configs
    get_repo_and_projects(
src/sentry/seer/fetch_issues/utils.py:100: in get_repo_and_projects
    raise NoProjectsForRepoError("No Sentry projects found for repo")
E   sentry.seer.fetch_issues.utils.NoProjectsForRepoError: No Sentry projects found for repo