Add 7 missing SDK methods and fix README type name

- Fix AgentKeyRequest → RegisterAgentKeyInput in README
- Add ListAgents, UnfreezeAgent, DeleteAgent to agents.go
- Add GetMe, IssueApiToken to auth.go
- Add DownloadExport to exports.go
- Add Health package-level function in health.go
- Add corresponding types and document all exports in README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

health.go

@@ -0,0 +1,62 @@
+package elydora
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// Health checks the health of the Elydora API. This is a public endpoint
+// that does not require authentication.
+func Health(baseURL string) (*HealthResponse, error) {
+	if baseURL == "" {
+		baseURL = defaultBaseURL
+	}
+	baseURL = strings.TrimRight(baseURL, "/")
+
+	client := &http.Client{Timeout: 30 * time.Second}
+	req, err := http.NewRequest(http.MethodGet, baseURL+"/v1/health", nil)
+	if err != nil {
+		return nil, fmt.Errorf("elydora: create request: %w", err)
+	}
+	req.Header.Set("Accept", "application/json")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("elydora: http request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	respBody, err := io.ReadAll(io.LimitReader(resp.Body, 10<<20))
+	if err != nil {
+		return nil, fmt.Errorf("elydora: read response body: %w", err)
+	}
+
+	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
+		var result HealthResponse
+		if err := json.Unmarshal(respBody, &result); err != nil {
+			return nil, fmt.Errorf("elydora: unmarshal response: %w", err)
+		}
+		return &result, nil
+	}
+
+	var errResp errorResponse
+	if err := json.Unmarshal(respBody, &errResp); err == nil && errResp.Error.Code != "" {
+		return nil, &ElydoraError{
+			StatusCode: resp.StatusCode,
+			Code:       errResp.Error.Code,
+			Message:    errResp.Error.Message,
+			RequestID:  errResp.Error.RequestID,
+			Details:    errResp.Error.Details,
+		}
+	}
+
+	return nil, &ElydoraError{
+		StatusCode: resp.StatusCode,
+		Code:       ErrorCodeInternalError,
+		Message:    string(respBody),
+	}
+}