feat: add anonymous access configuration for KV endpoints (issue #5)

- Add AllowAnonymousRead and AllowAnonymousWrite config parameters
- Set both to false by default for security
- Apply conditional authentication middleware to KV endpoints:
  - GET requires auth if AllowAnonymousRead is false
  - PUT requires auth if AllowAnonymousWrite is false
  - DELETE always requires authentication (no anonymous delete)
- Update integration tests to enable anonymous access for testing
- Maintain backward compatibility when AuthEnabled is false

🤖 Generated with [Claude Code](https://claude.ai/code)

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

types/types.go

@@ -273,4 +273,8 @@ type Config struct {
 	ClusteringEnabled      bool `yaml:"clustering_enabled"`       // Enable/disable clustering/gossip
 	RateLimitingEnabled    bool `yaml:"rate_limiting_enabled"`    // Enable/disable rate limiting
 	RevisionHistoryEnabled bool `yaml:"revision_history_enabled"` // Enable/disable revision history
+	
+	// Anonymous access control (Issue #5)
+	AllowAnonymousRead     bool `yaml:"allow_anonymous_read"`     // Allow unauthenticated read access to KV endpoints
+	AllowAnonymousWrite    bool `yaml:"allow_anonymous_write"`    // Allow unauthenticated write access to KV endpoints
 }