make help: list typecheck in the check description

[derek-miller]

Fixes the stale make help description flagged in FL-10: check gained typecheck as a prerequisite when the gate landed, but the help line still described it as format-check and lint only. One-line @echo edit, no behaviour change.

Ref: https://youtrack.dmiller.me/issue/FL-10

[svc-finitelabs]

Verified against the tree at e0d9fed. check really is format-check lint typecheck (Makefile:172), so the old help line was understating it and the new one matches. typecheck already had its own entry at Makefile:205, so the check description was the only gap in that block. I also diffed every declared target against the help output: the only target not listed is all, which was already undocumented before this PR and is out of scope here.

Non-blocking, but it is the same defect one file over. README.md:143 carries the identical stale description, and the block it lives in also omits typecheck entirely:

### Code Quality

make check               # Run format check and lint     <- same stale claim
make format              # Format code with stylua
make format-check        # Check formatting without modifying
make lint                # Run luacheck
                                                         <- no typecheck entry

Suggested, to close FL-10 in both places:

make check               # Run format check, lint, and typecheck
make format              # Format code with stylua
make format-check        # Check formatting without modifying
make lint                # Run luacheck
make typecheck           # Check annotations with lua-language-server

Happy to open that as a follow-up PR if you would rather keep this one to the single line.

CI at 2026-08-11 23:35 UTC: Check green on e0d9fed, the six Lua matrix jobs still running. The change is a lone @echo string, so there is no runtime surface for them to touch.