ci(ci): use pytestmon and Depot runners

[phernandez]

Summary

• Route the main justfile test recipes through pytest-testmon by default, with per-slice environments for SQLite, Postgres, semantic, and local runs.
• Add a shared pytest-testmon cache helper for worktrees and CI-style cache refreshes.
• Move Linux CI runners and Docker image publishing to Depot, while preserving Windows coverage on windows-latest.

Verification

• just --list
• uv run ruff check scripts/testmon_cache.py
• uv run ruff format --check scripts/testmon_cache.py
• YAML parse for .github/workflows/test.yml and .github/workflows/docker.yml
• go run github.com/rhysd/actionlint/cmd/actionlint@latest -ignore 'label "depot-ubuntu-24.04" is unknown' .github/workflows/test.yml .github/workflows/docker.yml\n- BASIC_MEMORY_TESTMON_FLAGS="--testmon-noselect" just testmon tests/ci/test_validate_skills.py -q\n- git diff --check\n\n## Notes\n- The Docker workflow expects DEPOT_BASIC_MEMORY_PROJECT_ID or DEPOT_PROJECT_ID to be configured for Depot builds.\n

Reviewed SHA: e3500233da4841de2f3f60d74f19b98eacbc514b
Verdict: approve
Status: success - BM Bossbot approved this head SHA

Summary:
Reviewed the full provided diff for head e350023. The previous blockers are addressed: required/full test recipes now default to --testmon-noselect, selective mode is isolated to just testmon, and the new testmon cache helper has focused regression coverage. No blocking issues remain.

Blocking findings:

• None

Non-blocking findings:

• Depot infrastructure still needs repository-level confirmation: The workflows now depend on the depot-ubuntu-24.04 runner label and Docker publishing expects DEPOT_BASIC_MEMORY_PROJECT_ID or DEPOT_PROJECT_ID. I did not find a diff-level correctness issue, but those org/repo settings are outside the provided context and should be confirmed operationally.