feat(core): add command, intent, and routing primitives

src/commands/index.ts

@@ -0,0 +1,11 @@
+export { CommandRegistry } from './registry.js';
+export type { CommandContext, CommandDefinition, CommandResult, CommandServices } from './types.js';
+export {
+  createHelpCommand,
+  createStatusCommand,
+  createUsageCommand,
+  createModelCommand,
+  createCompactCommand,
+  createResetCommand,
+  registerBuiltinCommands,
+} from './builtin/index.js';