Create or recover an execution job

Enabled only in configured local or staging execution cohorts. With quote-ID admission configured, accepts only {quote_id} and Idempotency-Key. The engine resolves and verifies the signed quote; the API atomically stores its immutable snapshot, accepted limits and signed submission deadline before queueing. Only eligible fee-aware DFlow Solana USDC routes are executable. Same accepted quote recovers its job even after expiry or Redis loss. An Idempotency-Key already bound to a different quote conflicts; alternate recovery keys are not stored as aliases. Legacy {quote_token} and raw preparation contracts retain their existing behavior.