docs: add README for workspace and all 7 crates

Root README covers architecture, Rust builder API quick start,
YAML pipeline quick start, provider table, deno executor overview,
feature flags, and testing instructions.

Per-crate READMEs follow consistent structure: one-liner, what it
does, quick start code example, API reference, configuration,
testing, license. Engineering-confident tone throughout.

wfe-core/README.md

@@ -0,0 +1,85 @@
+# wfe-core
+
+Core traits, models, builder, and executor for the WFE workflow engine.
+
+## What it does
+
+`wfe-core` defines the foundational abstractions that every other WFE crate builds on. It provides the `StepBody` trait for implementing workflow steps, a fluent `WorkflowBuilder` for composing workflow definitions, a `WorkflowExecutor` that drives step execution with locking and persistence, and a library of built-in control-flow primitives (if/while/foreach/parallel/saga).
+
+## Quick start
+
+Define a step by implementing `StepBody`, then wire steps together with the builder:
+
+```rust
+use async_trait::async_trait;
+use wfe_core::builder::WorkflowBuilder;
+use wfe_core::models::ExecutionResult;
+use wfe_core::traits::step::{StepBody, StepExecutionContext};
+
+#[derive(Default)]
+struct Greet;
+
+#[async_trait]
+impl StepBody for Greet {
+    async fn run(&mut self, _ctx: &StepExecutionContext<'_>) -> wfe_core::Result<ExecutionResult> {
+        println!("hello from a workflow step");
+        Ok(ExecutionResult::next())
+    }
+}
+
+let definition = WorkflowBuilder::<serde_json::Value>::new()
+    .start_with::<Greet>()
+    .name("greet")
+    .end_workflow()
+    .build("hello-workflow", 1);
+```
+
+## API
+
+| Type / Trait | Description |
+|---|---|
+| `StepBody` | The core unit of work. Implement `run()` to define step behavior. |
+| `StepExecutionContext` | Runtime context passed to each step (workflow data, persistence data, cancellation token). |
+| `WorkflowData` | Marker trait for data flowing between steps. Auto-implemented for anything `Serialize + DeserializeOwned + Send + Sync + Clone`. |
+| `WorkflowBuilder<D>` | Fluent builder for composing `WorkflowDefinition`s. Supports `start_with`, `then`, `if_do`, `while_do`, `for_each`, `parallel`, `saga`. |
+| `StepBuilder<D>` | Per-step builder returned by `WorkflowBuilder`. Configures name, error behavior, compensation. |
+| `WorkflowExecutor` | Acquires a lock, loads the instance, runs all active pointers, processes results, persists. |
+| `StepRegistry` | Maps step type names to factory functions. |
+| `PersistenceProvider` | Composite trait: `WorkflowRepository + EventRepository + SubscriptionRepository + ScheduledCommandRepository`. |
+| `DistributedLockProvider` | Trait for acquiring/releasing workflow-level locks. |
+| `QueueProvider` | Trait for enqueuing/dequeuing workflow and event work items. |
+
+### Built-in primitives
+
+| Primitive | Purpose |
+|---|---|
+| `IfStep` | Conditional branching |
+| `WhileStep` | Loop while condition holds |
+| `ForEachStep` | Iterate over a collection |
+| `SequenceStep` | Parallel branch container |
+| `DecideStep` | Multi-way branching |
+| `DelayStep` | Pause execution for a duration |
+| `ScheduleStep` | Resume at a specific time |
+| `WaitForStep` | Suspend until an external event |
+| `SagaContainerStep` | Transaction-like compensation |
+| `RecurStep` | Recurring/periodic execution |
+| `EndStep` | Explicit workflow termination |
+
+## Features
+
+| Feature | Description |
+|---|---|
+| `test-support` | Exposes `test_support` module with in-memory persistence and helpers for testing workflows. |
+| `otel` | Enables OpenTelemetry integration via `tracing-opentelemetry`. |
+
+## Testing
+
+```sh
+cargo test -p wfe-core
+```
+
+No external dependencies required.
+
+## License
+
+MIT