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>

README.md

@@ -0,0 +1,58 @@
+# VoiceCat
+
+Self-hosted, native voice & text chat in the spirit of classic TeamSpeak / Mumble —
+channel-based voice, channel + private text, one server you run yourself. Plain **TCP**
+(control) and **UDP** (media), no WebRTC. Encrypted by default. A shared **C++ core**
+(`libvoicecat`) drives native clients (Swift on macOS/iOS, C# on Windows) and the server.
+
+> **Status: pre-implementation.** The design is complete in [`docs/`](docs/). The code is an
+> M0 **skeleton** — it compiles and links, but every subsystem is a stub. See
+> [`AGENTS.md`](AGENTS.md) to start building, and [`docs/roadmap.md`](docs/roadmap.md) for the
+> milestones.
+
+## Read the design first
+
+The [`docs/`](docs/) folder is the source of truth. Start at [`docs/README.md`](docs/README.md),
+then `architecture` → `protocol` → `voice` → `security` → `tech-stack` → `deployment` →
+`roadmap`.
+
+## Build the skeleton (no dependencies needed yet)
+
+The M0 skeleton builds with just a C++20 compiler + CMake + Ninja — **no vcpkg, no
+third-party libraries**, because every subsystem is currently a stub.
+
+```bash
+cmake --preset dev
+cmake --build --preset dev
+ctest --preset dev            # runs the smoke test (links the core, calls the C ABI)
+```
+
+Artifacts land in `build/dev/bin/` (`voicecat-server`, `vccli`).
+
+When you start implementing a subsystem that needs real libraries, build with vcpkg deps:
+
+```bash
+# one-time: git clone https://github.com/microsoft/vcpkg && ./vcpkg/bootstrap-vcpkg.sh
+export VCPKG_ROOT=/path/to/vcpkg            # set VCPKG_ROOT (works on Linux/macOS/Windows)
+cmake --preset server-release               # auto-installs deps from vcpkg.json
+cmake --build --preset server-release
+```
+
+## Layout
+
+```
+docs/         design spec (read this)
+core/         libvoicecat — the shared C++ core
+  include/    voicecat.h  (the C ABI all clients call)
+  proto/      voicecat.proto  (control-plane wire format, source of truth)
+  src/        net/ crypto/ codec/ protocol/ session/ audio/  (stubs today)
+server/       voicecat-server (headless; links the core)
+tools/vccli/  headless test client — drives the protocol from M1 on
+clients/      apple/ (Swift, M4)   windows/ (C#, M4)   — placeholders for now
+tests/        CTest targets
+```
+
+## License
+
+Permissive-only dependencies (no GPL/LGPL) so the project can be redistributed freely,
+including closed-source. Project license: TBD (see [`docs/tech-stack.md`](docs/tech-stack.md) §5).