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>

tooling/project.cpp

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+// The build helper consumers load through
+//     #pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.Debug.git" project "tooling/project.cpp"
+// A separate project file because a pragma dependency is built for the host
+// and gets none of the consumer's args, so the root project.cpp could not
+// tell this load from the one that builds the library for the target.
+//
+// No dependency on Crafter.Build, as in Crafter.LintRules: this module only
+// ever runs inside a crafter-build process, which provides the symbols, and
+// the host build already sees the Crafter.Build modules through the PCM cache
+// crafter-build keeps for project files. Nor on anything else: whatever this
+// imported would be built on every load of every consumer.
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    Configuration cfg;
+    cfg.path = "./";
+    cfg.name = "Crafter.Debug.Build";
+    cfg.outputName = "Crafter.Debug.Build";
+    cfg.type = ConfigurationType::LibraryStatic;
+    ApplyStandardArgs(cfg, args);
+    std::array<fs::path, 1> interfaces = { "interfaces/Crafter.Debug.Build" };
+    std::array<fs::path, 0> implementations = {};
+    cfg.GetInterfacesAndImplementations(interfaces, implementations);
+    return cfg;
+}