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>

CMakePresets.json

@@ -0,0 +1,42 @@
+{
+  "version": 6,
+  "cmakeMinimumRequired": { "major": 3, "minor": 25, "patch": 0 },
+  "configurePresets": [
+    {
+      "name": "dev",
+      "displayName": "Dev (skeleton, no third-party deps)",
+      "description": "Builds the stub skeleton with just a compiler. Works out of the box; no vcpkg required.",
+      "generator": "Ninja",
+      "binaryDir": "${sourceDir}/build/dev",
+      "cacheVariables": {
+        "CMAKE_BUILD_TYPE": "Debug",
+        "VOICECAT_USE_VCPKG_DEPS": "OFF"
+      }
+    },
+    {
+      "name": "vcpkg-base",
+      "hidden": true,
+      "description": "Shared base for presets that link real deps via vcpkg. Requires VCPKG_ROOT in the environment.",
+      "generator": "Ninja",
+      "toolchainFile": "$env{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake",
+      "cacheVariables": { "VOICECAT_USE_VCPKG_DEPS": "ON" }
+    },
+    {
+      "name": "server-release",
+      "inherits": "vcpkg-base",
+      "displayName": "Server (release, real deps)",
+      "binaryDir": "${sourceDir}/build/server-release",
+      "cacheVariables": {
+        "CMAKE_BUILD_TYPE": "Release",
+        "VOICECAT_BUILD_TOOLS": "ON"
+      }
+    }
+  ],
+  "buildPresets": [
+    { "name": "dev",            "configurePreset": "dev" },
+    { "name": "server-release", "configurePreset": "server-release" }
+  ],
+  "testPresets": [
+    { "name": "dev", "configurePreset": "dev", "output": { "outputOnFailure": true } }
+  ]
+}