scaffold: M0 skeleton + agent onboarding (build, architecture, progress)

Turn the design into a buildable, dependency-free M0 skeleton plus the
onboarding layer so a new agent can pick up instantly.

Build system:
- CMake + CMakePresets (dev = no deps; server-release = vcpkg) + vcpkg.json
- Skeleton builds with just a C++20 compiler; deps stay off until needed
- .gitattributes (LF), .gitignore, .clang-format

Core (libvoicecat):
- core/include/voicecat.h: full C ABI (the client/server contract), stubbed
- core/proto/voicecat.proto: control-plane wire format, matches docs/protocol.md
- src/{net,crypto,codec,protocol,session,audio,core}: subsystem stubs that
  return VC_ERR_NOT_IMPLEMENTED, each pointing to its design doc
- server/ (voicecat-server) and tools/vccli/ link the core
- tests/: CTest smoke test asserting the C ABI contract (behavior, not just build)
- clients/{apple,windows}: M4 placeholders

Onboarding for agents:
- CLAUDE.md: hub — build/test commands, architecture at a glance, doc map, rules
- AGENTS.md: working method (behavior-driven; clean compile is the floor not the goal)
- PROGRESS.md: living tracker — M0 done, M1 task checklist, "where we left off"

Verified: cmake --preset dev && cmake --build --preset dev && ctest --preset dev → green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/server.cpp

@@ -0,0 +1,20 @@
+#include "server.h"
+
+#include <cstdio>
+
+namespace voicecat::server {
+
+int Server::run() {
+    // M0 stub: report what a real run WILL do, then exit. M1 brings up the TLS listener,
+    // session registry, and channel manager (docs/architecture.md §5).
+    std::printf("  server_name : %s\n", cfg_.server_name.c_str());
+    std::printf("  data_dir    : %s\n", cfg_.data_dir.c_str());
+    std::printf("  bind_port   : %u (TCP control + UDP media)\n", cfg_.bind_port);
+    std::printf("  allow_guests: %s\n", cfg_.allow_guests ? "true" : "false");
+    std::printf("  fingerprint : <generated on first run — TODO M1>\n");
+    std::printf("\n[voicecat-server] M0 skeleton: networking not implemented yet. "
+                "See docs/roadmap.md (M1) and AGENTS.md.\n");
+    return 0;
+}
+
+}  // namespace voicecat::server