feat(tooling): wire consumers in through Debug::Use and a launcher

A consumer loads Crafter.Debug.Build through
  #pragma crafter dependency "<Crafter.Debug>" project "tooling/project.cpp"
and calls Debug::Use in its own CrafterBuildProject, the way
Crafter.LintRules gets in. With the consumer's flag on, Use adds the
library from the checkout the pragma loaded, and writes
build/crafter-debug: a POSIX sh launcher for the client that library
builds. The client is one of the library's dependencies, so a debug
build compiles it in the same pass as the app, from the same sources.

Why a launcher and not a script: every `crafter-build run` loads the
whole project first, which costs 13-28 s per call on 3DForts (a git
pull per unpinned dependency plus rescanning sources), while the
launcher is one sandbox start, 0.08 s. A client built in the Flatpak
links the Flatpak's libc++ against the runtime's glibc, so the launcher
starts it through `flatpak run` and never on the host itself; inside a
CrafterBuild sandbox it runs it directly.

The library, the client and examples/Basic are placeholders that prove
the wiring: the debug build writes a launcher whose client exists, a
plain build has no Crafter::Debug symbols and keeps the notes from
tooling/AGENTS.consumer.md, and a fresh plain build writes a stub that
names the flag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/Basic/implementations/main.cpp

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+#ifdef BASIC_DEBUG_API
+import Crafter.Debug;
+#endif
+
+int main() {
+#ifdef BASIC_DEBUG_API
+    std::println("basic: debug build, Crafter.Debug {}", Crafter::Debug::Version());
+#else
+    std::println("basic: plain build");
+#endif
+    return 0;
+}