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.h

@@ -0,0 +1,40 @@
+/*
+ * server.h — voicecat-server skeleton.
+ *
+ * Design: docs/architecture.md §5, docs/deployment.md. Headless process that links the core.
+ * Responsibilities: connection manager (TLS), session registry, channel manager, text router,
+ * voice SFU relay, SQLite persistence. Zero-config: self-provisions Ed25519 identity + cert
+ * on first run, embedded SQLite, guests on by default.
+ *
+ * STATUS: M0 stub — prints config and exits; does not yet listen.
+ */
+#ifndef VOICECAT_SERVER_SERVER_H
+#define VOICECAT_SERVER_SERVER_H
+
+#include <cstdint>
+#include <string>
+
+namespace voicecat::server {
+
+struct Config {
+    std::string server_name = "VoiceCat Server";
+    std::string data_dir = "voicecat-data";
+    uint16_t bind_port = 8384;   // TCP + UDP (docs/deployment.md §2)
+    bool allow_guests = true;
+};
+
+class Server {
+   public:
+    explicit Server(Config cfg) : cfg_(std::move(cfg)) {}
+
+    // TODO(M1): bind TLS control listener + UDP media socket; run the Asio loop until stop.
+    // Returns process exit code.
+    int run();
+
+   private:
+    Config cfg_;
+};
+
+}  // namespace voicecat::server
+
+#endif  // VOICECAT_SERVER_SERVER_H