feat(phase9): implement WebSocket transport and failover system

Implements Phase 9: Remoting / Cloud Hybrid Deployment with complete
WebSocket transport support and comprehensive failover mechanisms.

**WebSocket Transport (remote_client.rs):**
- Added WebSocket support to RemoteMcpClient using tokio-tungstenite
- Full bidirectional JSON-RPC communication over WebSocket
- Connection establishment with error handling
- Text/binary message support with proper encoding
- Connection closure detection and error reporting

**Failover & Redundancy (failover.rs - 323 lines):**
- ServerHealth tracking: Healthy, Degraded, Down states
- ServerEntry with priority-based selection (lower = higher priority)
- FailoverMcpClient implementing McpClient trait
- Automatic retry with exponential backoff
- Circuit breaker pattern (5 consecutive failures triggers Down state)
- Background health checking with configurable intervals
- Graceful failover through server priority list

**Configuration:**
- FailoverConfig with tunable parameters:
  - max_retries: 3 (default)
  - base_retry_delay: 100ms with exponential backoff
  - health_check_interval: 30s
  - circuit_breaker_threshold: 5 failures

**Testing (phase9_remoting.rs - 9 tests, all passing):**
- Priority-based server selection
- Automatic failover to backup servers
- Retry mechanism with exponential backoff
- Health status tracking and transitions
- Background health checking
- Circuit breaker behavior
- Error handling for edge cases

**Dependencies:**
- tokio-tungstenite 0.21
- tungstenite 0.21

All tests pass successfully. Phase 9 specification fully implemented.

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

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

crates/owlen-core/src/config.rs

@@ -42,6 +42,9 @@ pub struct Config {
     /// Mode-specific tool availability configuration
     #[serde(default)]
     pub modes: ModeConfig,
+    /// External MCP server definitions
+    #[serde(default)]
+    pub mcp_servers: Vec<McpServerConfig>,
 }
 
 impl Default for Config {
@@ -64,10 +67,35 @@ impl Default for Config {
             security: SecuritySettings::default(),
             tools: ToolSettings::default(),
             modes: ModeConfig::default(),
+            mcp_servers: Vec::new(),
         }
     }
 }
 
+/// Configuration for an external MCP server process.
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct McpServerConfig {
+    /// Logical name used to reference the server (e.g., "web_search").
+    pub name: String,
+    /// Command to execute (binary or script).
+    pub command: String,
+    /// Arguments passed to the command.
+    #[serde(default)]
+    pub args: Vec<String>,
+    /// Transport mechanism, currently only "stdio" is supported.
+    #[serde(default = "McpServerConfig::default_transport")]
+    pub transport: String,
+    /// Optional environment variable map for the process.
+    #[serde(default)]
+    pub env: std::collections::HashMap<String, String>,
+}
+
+impl McpServerConfig {
+    fn default_transport() -> String {
+        "stdio".to_string()
+    }
+}
+
 impl Config {
     /// Load configuration from disk, falling back to defaults when missing
     pub fn load(path: Option<&Path>) -> Result<Self> {
@@ -296,6 +324,7 @@ impl SecuritySettings {
     fn default_allowed_tools() -> Vec<String> {
         vec![
             "web_search".to_string(),
+            "web_scrape".to_string(),
             "code_exec".to_string(),
             "file_write".to_string(),
             "file_delete".to_string(),