Remove unused stub files: forth/, words/, compiler.rs, primitives.rs, types.rs

All were planning artifacts never imported or loaded:
- forth/ (4 .fth files): commented-out TODO stubs, never loaded at startup
- crates/core/src/words/mod.rs: empty module with commented-out submodules
- compiler.rs: placeholder, all compiler logic lives in outer.rs
- primitives.rs: placeholder, all primitives registered in outer.rs
- types.rs: StackType/StackEffect defined but never imported anywhere

crates/core/src/lib.rs

@@ -11,13 +11,10 @@
 //!
 //! The compilation pipeline:
 //! 1. **Outer interpreter** tokenizes input and dispatches to interpret/compile mode
-//! 2. **Compiler** builds an intermediate representation (IR) for each word definition
-//! 3. **Type inference** annotates the IR with stack types
-//! 4. **Optimizer** applies transformation passes (constant folding, inlining, etc.)
-//! 5. **Codegen** translates optimized IR to WASM bytecode via `wasm-encoder`
+//! 2. **Optimizer** applies transformation passes (constant folding, inlining, etc.)
+//! 3. **Codegen** translates optimized IR to WASM bytecode via `wasm-encoder`
 
 pub mod codegen;
-pub mod compiler;
 pub mod config;
 pub mod consolidate;
 pub mod dictionary;
@@ -26,6 +23,3 @@ pub mod ir;
 pub mod memory;
 pub mod optimizer;
 pub mod outer;
-pub mod primitives;
-pub mod types;
-pub mod words;