feat: add cli-based LLM provider

Add ClaudeCliProvider that executes the local CLI as a subprocess,
enabling PicoClaw to leverage advanced capabilities (MCP tools,
workspace awareness, session management) through any messaging channel.

- Implement LLMProvider interface via subprocess execution
- Support --system-prompt, --model, --output-format json flags
- Parse real v2.x JSON response format including usage tokens
- Handle error responses, stderr, context cancellation
- Register "claude-cli", "claude-code", "claudecode" aliases in CreateProvider
- 56 unit tests with mock scripts + 3 integration tests against real binary
- 100% coverage on all functions except stripToolCallsJSON (85.7%)

pkg/providers/http_provider.go

@@ -289,6 +289,12 @@ func CreateProvider(cfg *config.Config) (LLMProvider, error) {
 				apiKey = cfg.Providers.VLLM.APIKey
 				apiBase = cfg.Providers.VLLM.APIBase
 			}
+		case "claude-cli", "claudecode", "claude-code":
+			workspace := cfg.Agents.Defaults.Workspace
+			if workspace == "" {
+				workspace = "."
+			}
+			return NewClaudeCliProvider(workspace), nil
 		}
 	}