rename crates/ to engrams/, bindings/ to receptors/

- crates/ → engrams/ (Rust engrams live here)
- bindings/ → receptors/ (cross-language access points into the graph)
- Cargo.toml workspace paths updated

engrams/engram-projection/src/lib.rs

@@ -0,0 +1,33 @@
+/// Engram Projection Layer — schema-as-a-view over the activation surface.
+///
+/// # The Core Insight
+///
+/// Engram has no schema. A node has: embedding (semantic identity), content
+/// (arbitrary bytes), metadata via tier/type, and salience. Schema is a
+/// *projection* — a view imposed on the activation surface at query time.
+///
+/// The same Engram graph can surface as relational rows, JSON documents,
+/// wide-column families, or key-value pairs depending on how you project it.
+/// Migrations are free because there is nothing to migrate — you just update
+/// the projection.
+///
+/// # How It Works
+///
+/// 1. Register a `ProjectionSchema` that describes which nodes are in scope
+///    and how to map their fields.
+/// 2. At query time, run spreading activation (or use an existing result set).
+/// 3. Apply the projection to map `ActivatedNode`s into the projected view.
+///
+/// The projection is purely a read-time transform. It never modifies the graph.
+pub mod engine;
+pub mod error;
+pub mod registry;
+pub mod schema;
+
+pub use engine::ProjectionEngine;
+pub use error::ProjectionError;
+pub use registry::ProjectionRegistry;
+pub use schema::{
+    FieldMapping, FieldSource, NodeFilter, ProjectedRow, ProjectionResult, ProjectionSchema,
+    ProjectionType,
+};