selfhost: migrate tool sources to directory packages

Build w6a and w6l from package-main directories and expose the wcc backend through a narrow package API so w6c and wwdump no longer import implementation files. Retarget the remaining load-bearing fixtures and example sources to directory packages; retain the one intentional flat compiler collision as an explicitly composed raw unit.

examples/lisp/CLAUDE.md

@@ -5,7 +5,7 @@ backend rather than the C bootstrap one.
 
 ## Layout
 
-- `lispcore.ww`     interpreter module: types, lexer, parser, env,
+- `lispcore/`       interpreter directory package: types, lexer, parser, env,
                     eval, apply, printer, REPL. Everything the entry
                     point and the test driver consume is `export`-ed.
 - `lisp.ww`         entry point; `use lispcore;` + `main()`.
@@ -15,12 +15,9 @@ backend rather than the C bootstrap one.
                     runs the binary itself.
 - `test_*.lisp`     demo source files (`cat test_X.lisp | ./lisp`).
 
-The lispcore.ww + lisp.ww split exists so the tests can `use` the
-interpreter functions. Both files combine under the same module name
-(the directory's basename, `lisp`), because `ww`'s module resolver
-takes the *containing-directory* basename when finding a sibling.
-Cross-module type prefixes like `lispcore.value` don't resolve in the
-test — use the bare names.
+The lispcore/ + lisp.ww split exists so the entry point and tests import
+one canonical interpreter directory package. Cross-module type prefixes
+like `lispcore.value` don't resolve in the test — use the bare names.
 
 ## wwstage cgen workarounds at play