FlowFabric — umbrella crate re-exporting the published crate family.

Pin one crate; let Cargo resolve the rest. Closes #279 — prior to v0.8.2 consumers (cairn-fabric, downstream integrations) had to pin all 7–8 ff-* crates + ferriskey in lockstep and version- skew drift was only caught at cargo update time. This crate is the single-line import surface; feature flags gate which backend and which optional internals get pulled in.

Quick start

# Valkey backend (default):
flowfabric = "0.8"

# Postgres backend (explicit, no valkey):
flowfabric = { version = "0.8", default-features = false, features = ["postgres"] }

# Advanced — direct engine/scheduler access:
flowfabric = { version = "0.8", features = ["engine", "scheduler-internals"] }

See docs/CONSUMER_MIGRATION_v0.8.md § "Umbrella crate (flowfabric)" for mapping from the 7-crate import shape to the umbrella shape.

Re-export map

The prelude module glob-re-exports the 80% path (flowfabric::sdk::*), which already flattens the most-used ff_core::contracts and ff_core::backend types via ff-sdk's own pub use. Consumers needing scheduler/engine types should enable the respective feature flag and reach through flowfabric::engine::… / flowfabric::scheduler::… explicitly.