feat(config): T-1260 — reach lists its domains without importing them

`reach --help` renders from a declaration table and imports nothing. The cost
of help is now flat as the registry grows, which is the property that has to
hold going from one domain to a dozen.

The trap is real and was confirmed in typer's vendored source rather than
assumed from upstream Click: TyperGroup.format_commands loops over
list_commands calling get_command on each, purely to read a short help string
off the loaded command. With lazy loading underneath, that imports every
domain in the registry to render --help — while the output looks entirely
correct. Nothing observable changes; only the import graph does.

So the test asserts on sys.modules, and it was proven to fail before being
trusted. Disabling the format_commands override made it fail and name the
cause, listing all five leaked check modules. It also carries a positive
control — invoking a domain must import its service — because without one,
"nothing was imported" would pass equally for a loader that is simply broken,
and it fails on an empty registry, which would otherwise satisfy everything
vacuously.

The check domain is created here because the test needs a subject: a stub
raising NotImplementedError would have been committed dead code. That takes
the port out of T-1262, which is rescoped to what it still owns — pydantic
schemas, byte-for-byte output parity on the drift path, and the failure
tests. The old tooling/check-client-version script stays in place and stays
wired to the pre-push hook; the deprecation window is deliberate.

One Typer behaviour worth knowing before every future domain: a single-command
app collapses into a bare command, so `reach check client-version` failed with
"unexpected extra argument" until the router got a callback. Same mechanism as
the root callback, different symptom.

Help now works at every level, closing item 5 of T-1248.

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

Makefile

@@ -268,6 +268,10 @@ test-tooling:
 	@mkdir -p .cache
 	@python3 tooling/test_canvas_version_check.py 2> .cache/test-tooling-canvas-version.log || \
 		{ echo "  FAIL: canvas version gate units — log follows:"; cat .cache/test-tooling-canvas-version.log; exit 1; }
+	@echo "  [test-tooling] reach lazy domain registration (T-1260)..."
+	@mkdir -p .cache
+	@$(VENV_PY) tooling/test_lazy_domains.py 2> .cache/test-tooling-lazy-domains.log || \
+		{ echo "  FAIL: reach lazy registration — log follows:"; cat .cache/test-tooling-lazy-domains.log; exit 1; }
 	@echo "  [test-tooling] economy_import.traits validation units (T-995/PR #173 H2)..."
 	@mkdir -p .cache
 	@python3 tooling/economy-db/test_traits.py 2> .cache/test-tooling-traits.log || \