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>

vcpkg.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://raw.githubusercontent.com/microsoft/vcpkg/master/scripts/vcpkg.schema.json",
+  "name": "voicecat",
+  "version": "0.0.1",
+  "description": "Self-hosted native voice & text chat. See docs/.",
+  "builtin-baseline": "0000000000000000000000000000000000000000",
+  "$comment-baseline": "TODO: set builtin-baseline to a real vcpkg commit SHA when first enabling VOICECAT_USE_VCPKG_DEPS. Until then the skeleton builds with deps OFF and this manifest is inert.",
+  "dependencies": [
+    { "name": "opus",                    "$why": "voice codec (libopus 1.6) — docs/voice.md" },
+    { "name": "libsodium",               "$why": "Argon2id, ChaCha20-Poly1305 media AEAD, Ed25519 — docs/security.md" },
+    { "name": "mbedtls",                 "$why": "TLS 1.3 control channel + keying-material exporter — docs/security.md" },
+    { "name": "protobuf",                "$why": "control-plane serialization — docs/protocol.md" },
+    { "name": "sqlite3",                 "$why": "server accounts/state — docs/security.md" },
+    { "name": "asio",                    "$why": "TCP/UDP/timers reactor — docs/architecture.md" },
+    { "name": "miniaudio",               "$why": "cross-platform capture/playback — docs/tech-stack.md" },
+    { "name": "speexdsp",                "$why": "resampling + jitter reference — docs/tech-stack.md" },
+    { "name": "webrtc-audio-processing", "$why": "AEC/NS/AGC/VAD (APM) — docs/voice.md" },
+    { "name": "spdlog",                  "$why": "logging — docs/tech-stack.md" }
+  ],
+  "$license-note": "All of the above are permissive (BSD/MIT/ISC/Apache-2.0/public-domain). No GPL/LGPL — see docs/tech-stack.md §5."
+}