restructure: move search.rs and query.rs into query/ directory

search.rs → query/engine.rs (algorithms, pipeline, seed matching)
query.rs  → query/parser.rs (PEG query language, field resolution)
query/mod.rs re-exports for backwards compatibility.

crate::search still works (aliased to query::engine).
crate::query::run_query resolves to the parser's entry point.

No logic changes — pure file reorganization.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/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;