chore(release): secrets-mcp 0.4.0

Bump version for the N:N entry_secrets data model and related MCP/Web
changes. Remove superseded SQL migration artifacts; rely on auto-migrate.
Add structured errors, taxonomy normalization, and web i18n helpers.

Made-with: Cursor

crates/secrets-mcp/src/error.rs

@@ -0,0 +1,36 @@
+use secrets_core::error::AppError;
+
+/// Map a structured `AppError` to an MCP protocol error.
+///
+/// This replaces the previous pattern of swallowing all errors into `-32603`.
+pub fn app_error_to_mcp(err: &AppError) -> rmcp::ErrorData {
+    match err {
+        AppError::ConflictSecretName { secret_name } => rmcp::ErrorData::invalid_request(
+            format!(
+                "A secret with the name '{secret_name}' already exists for your account. \
+                 Secret names must be unique per user."
+            ),
+            None,
+        ),
+        AppError::ConflictEntryName { folder, name } => rmcp::ErrorData::invalid_request(
+            format!(
+                "An entry with folder='{folder}' and name='{name}' already exists. \
+                 The combination of folder and name must be unique."
+            ),
+            None,
+        ),
+        AppError::NotFoundEntry => rmcp::ErrorData::invalid_request(
+            "Entry not found. Use secrets_find to discover existing entries.",
+            None,
+        ),
+        AppError::Validation { message } => rmcp::ErrorData::invalid_request(message.clone(), None),
+        AppError::ConcurrentModification => rmcp::ErrorData::invalid_request(
+            "The entry was modified by another request. Please refresh and try again.",
+            None,
+        ),
+        AppError::Internal(_) => rmcp::ErrorData::internal_error(
+            "Request failed due to a server error. Check service logs if you need details.",
+            None,
+        ),
+    }
+}