flatten: move poc-memory contents to workspace root

No more subcrate nesting — src/, agents/, schema/, defaults/, build.rs
all live at the workspace root. poc-daemon remains as the only workspace
member. Crate name (poc-memory) and all imports unchanged.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/query/mod.rs

@@ -0,0 +1,13 @@
+// query/ — query parsing, search algorithms, and pipeline execution
+//
+// parser.rs  — PEG-based query language (key ~ 'foo' | sort degree | limit 10)
+// engine.rs  — search algorithms: spreading activation, spectral, geodesic,
+//              manifold, confluence. Query DSL execution. Seed matching.
+
+pub mod parser;
+pub mod engine;
+
+// Re-export parser's run_query as the main query entry point
+// (engine::run_query is the internal search pipeline, accessed via crate::search)
+pub use parser::run_query;
+pub use parser::execute_query;