feat: add Linear OAuth integration and connector routes

- Introduced Linear OAuth support with new environment variables for client ID, client secret, and redirect URI.
- Implemented Linear connector routes for OAuth flow, including authorization and callback handling.
- Updated existing components to accommodate Linear integration, including validation changes and connector configuration.
- Enhanced the Linear indexer to utilize OAuth access tokens instead of API keys.
- Adjusted UI components to reflect the new Linear connector without requiring special configuration.

surfsense_web/components/assistant-ui/connector-popup/hooks/use-connector-dialog.ts

@@ -472,7 +472,7 @@ export const useConnectorDialog = () => {
 							}
 
 							// Auto-start indexing for non-OAuth reindexable connectors
-							// This only applies to non-OAuth reindexable connectors (e.g., Elasticsearch, Linear)
+							// This only applies to non-OAuth reindexable connectors (e.g., Elasticsearch)
 							// Non-reindexable connectors (e.g., Tavily) have is_indexable: false, so they won't trigger this
 							// Backend will use default date ranges (365 days ago to today) if dates are not provided
 							if (connector.is_indexable) {