refactor(runtime): make failure policy authoritative

[daniele21]

RA-4D — authoritative failure classification and recovery telemetry

Closes the remaining duplicate failure-classification path in RuntimeOrchestrator.

Changes

• RuntimeFailurePolicy now resolves backend failures into a stable public error + internal family/recovery decision;
• non-configuration backend codes/messages no longer become public error contracts;
• storage/integrity failures map to the existing stable MODEL_UNAVAILABLE public category;
• RuntimeOrchestrator consumes the canonical policy instead of maintaining its own hard-coded backend-code switch;
• runtime failure telemetry records failureFamily, recovery, automaticRetryLimit and only a strictly sanitized technical backend code;
• no prompt/output/backend free-form message is added to telemetry;
• automatic retry remains disabled (0) everywhere.

Evidence

Focused policy and telemetry tests cover stable public mapping, private-detail non-disclosure, recovery fields, backend-code normalization/sanitization, and the no-auto-retry invariant.

Gate

Keep draft until exact-head runtime-core compile/unit/Spotless/Detekt and repository validation are green against current dev.