feat: implement advanced condition-based heuristic model routing

Upgrades the routing engine to support tag, token limit, multimodal, reasoning, and tool calling conditions. Adds unit tests for the new routing features.

internal/db/db.go

@@ -32,6 +32,14 @@ func Init(path string) (*DB, error) {
 		return nil, fmt.Errorf("failed to connect to database: %w", err)
 	}
 
+	// Enable Write-Ahead Logging (WAL) and set a busy timeout to handle concurrent access
+	if _, err := db.Exec("PRAGMA journal_mode=WAL;"); err != nil {
+		log.Printf("failed to enable WAL mode: %v", err)
+	}
+	if _, err := db.Exec("PRAGMA busy_timeout=5000;"); err != nil {
+		log.Printf("failed to set busy timeout: %v", err)
+	}
+
 	instance := &DB{db}
 
 	// Run migrations