Check the reference corpus in, so the build stops needing the Go submodule

All 41 .bas/.txt pairs copied byte for byte from basicinterpreter@d76162c into
tests/reference/, plus the Commodore font into assets/fonts/ -- the two things
that tied the build to deps/basicinterpret. Both were verified cmp-identical
to the submodule copies.

This reverses a decision that was deliberate and correct at the time: the
corpus was driven in place because copying a submodule's corpus guarantees
drift. Overruled on purpose -- the Go dependency is being deprecated, and a
build that cannot run its acceptance suite without cloning the implementation
it replaced is not finished. tests/reference/README.md records what the drift
now costs and that those expectations are never edited.

Checked rather than assumed: both configurations configure, build and pass
from scratch with deps/basicinterpret moved out of the tree entirely.

The submodule is kept as the behavioural spec, which is a real use. The font
came with an open licence question; assets/fonts/PROVENANCE.md states it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -190,10 +190,17 @@ make tests               # or: bash ./test.sh
 stdout against the sibling `.txt`. The exit code is the number of failures. To run a single case,
 just run the interpreter on that `.bas` and diff against its `.txt`.
 
-That corpus is the natural acceptance suite for the rewrite: the C interpreter should reproduce the
-same stdout for the same `.bas` files. Carry it over (or drive it in place) alongside the per-module
-CTest executables the `ak*` style calls for — the two answer different questions, and new language
-features from goal 2 need a `.bas`/`.txt` pair as well as unit tests.
+That corpus is the acceptance suite for the rewrite: the C interpreter reproduces the same stdout
+for the same `.bas` files. **It has been copied into this repository at `tests/reference/`** and no
+longer runs out of the submodule — see `tests/reference/README.md` for the provenance and for the
+rule that those expectations are never edited to suit this interpreter. It sits alongside the
+per-module CTest executables the `ak*` style calls for; the two answer different questions, and new
+language features from goal 2 need a `.bas`/`.txt` pair in `tests/language/` as well as unit tests.
+
+**`deps/basicinterpret` is no longer a build or test dependency.** Both configurations were
+configured, built and run from scratch with it moved out of the tree. It is kept only as the
+behavioural spec to read when a question about semantics comes up — which is a real use, and the
+reason it has not been removed. The Commodore font it also supplied now lives in `assets/fonts/`.
 
 `deps/basicinterpret/README.md` is the language reference — implemented verbs, functions, variable
 type suffixes, and an explicit list of what is *not* implemented. Read it before adding or porting