feat(api): add llama.cpp support as local model provider

- Add llamacpp provider preset to provider-presets.ts
- Add base-llamacpp.settings.json configuration
- Update help-command.ts with ccs llamacpp documentation
- Update UI provider presets for dashboard parity

llama.cpp is a popular C++ inference engine for LLaMA models.
This complements existing Ollama support for local inference.

Usage: ccs llamacpp (requires llama.cpp server on port 8080)

Closes #690

config/base-llamacpp.settings.json

@@ -0,0 +1,10 @@
+{
+  "env": {
+    "ANTHROPIC_BASE_URL": "http://127.0.0.1:8080",
+    "ANTHROPIC_AUTH_TOKEN": "llamacpp",
+    "ANTHROPIC_MODEL": "llama3-8b",
+    "ANTHROPIC_DEFAULT_OPUS_MODEL": "llama3-70b",
+    "ANTHROPIC_DEFAULT_SONNET_MODEL": "llama3-8b",
+    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "llama3-2b"
+  }
+}