refactor(ml): remove stub ErrorCategory, use common::error::ErrorCategory

The ml crate had a stub ErrorCategory with only 1 variant (System).
Replace it with a re-export of the canonical 24-variant ErrorCategory
from common::error. Also rename the unused ErrorCategory in
data/src/providers/common.rs to ProviderErrorCategory to avoid
name collision.

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

data/src/providers/common.rs

@@ -47,14 +47,14 @@ use serde::{Deserialize, Serialize};
 /// # Examples
 ///
 /// ```rust
-/// use data::providers::common::ErrorCategory;
+/// use data::providers::common::ProviderErrorCategory;
 ///
 /// match error_category {
-///     ErrorCategory::RateLimit => {
+///     ProviderErrorCategory::RateLimit => {
 ///         // Implement exponential backoff
 ///         tokio::time::sleep(Duration::from_millis(1000)).await;
 ///     },
-///     ErrorCategory::Authentication => {
+///     ProviderErrorCategory::Authentication => {
 ///         // Refresh credentials and reconnect
 ///         provider.refresh_auth().await?;
 ///     },
@@ -64,7 +64,7 @@ use serde::{Deserialize, Serialize};
 /// }
 /// ```
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
-pub enum ErrorCategory {
+pub enum ProviderErrorCategory {
     /// Network connectivity issues, WebSocket disconnections
     ///
     /// Indicates problems with the underlying network connection to the

ml/src/lib.rs

@@ -457,15 +457,8 @@ impl CommonError {
     }
 }
 
-/// Error categories for system-wide error classification
-///
-/// This enum provides a way to categorize errors across the entire system,
-/// enabling better error handling, logging, and monitoring strategies.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
-pub enum ErrorCategory {
-    /// System-level errors including hardware, network, and infrastructure issues
-    System,
-}
+// Re-export canonical ErrorCategory from common crate (24 variants)
+pub use ::common::error::ErrorCategory;
 
 // Now using real types from common crate