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>

integration_test.sh

@@ -91,6 +91,8 @@ port: 8090
 data_dir: "./basic_data"
 seed_nodes: []
 log_level: "error"
+allow_anonymous_read: true
+allow_anonymous_write: true
 EOF
     
     # Start node
@@ -134,6 +136,8 @@ log_level: "error"
 gossip_interval_min: 5
 gossip_interval_max: 10
 sync_interval: 10
+allow_anonymous_read: true
+allow_anonymous_write: true
 EOF
     
     # Node 2 config
@@ -147,6 +151,8 @@ log_level: "error"
 gossip_interval_min: 5
 gossip_interval_max: 10
 sync_interval: 10
+allow_anonymous_read: true
+allow_anonymous_write: true
 EOF
     
     # Start nodes
@@ -242,6 +248,8 @@ data_dir: "./conflict1_data"
 seed_nodes: []
 log_level: "info"
 sync_interval: 3
+allow_anonymous_read: true
+allow_anonymous_write: true
 EOF
         
         cat > conflict2.yaml <<EOF
@@ -252,6 +260,8 @@ data_dir: "./conflict2_data"
 seed_nodes: ["127.0.0.1:8111"]
 log_level: "info"
 sync_interval: 3
+allow_anonymous_read: true
+allow_anonymous_write: true
 EOF
         
         # Start nodes