Add privacy-safe automation failure signals

[abrichr]

Outcome

• adds a closed categorical openadapt.automation-failure-signal/v1 envelope for recurring runtime, drift, identity, actuation, effect, and over-halt discovery
• derives the recurrence signature only from enums; application, tenant, workflow, step, origin, free text, inputs, screenshots, exception detail, and evidence never enter the API
• groups aggregate events by the failure signature rather than the installation/user distinct ID
• preserves DO_NOT_TRACK and existing telemetry opt-out semantics
• explicitly keeps repair authorization and promotion outside telemetry

Verification

• PYTHONPATH=src python -m pytest -q (122 passed)
• PYTHONPATH=src python -m ruff check src tests
• focused tests cover deterministic coarse signatures, fail-closed inputs, no installation ID egress, and opt-out

Boundary

This is the public mechanism/interface only. Cross-customer corpus, recurrence thresholds, ranking, and repair recipes remain private.