fix(core): default to 'run' target when only project is specified (#31452)

## Current Behavior

When running `nx run <project>` without specifying a target, the command
always fails with an error message "Both project and target have to be
specified", even if the project has a "run" target defined.

## Expected Behavior

When running `nx run <project>` without specifying a target, the command
should check if the project has a "run" target defined. If it does, use
it as the default target. This improves developer experience by allowing
simpler commands like `nx run myapp` instead of `nx run myapp:run`.

## Related Issue(s)

This change improves the developer experience for projects that have a
"run" target defined, making the CLI more intuitive.

## Changes Made

- Modified `packages/nx/src/command-line/run/run-one.ts` to check for a
"run" target when no target is specified
- Added comprehensive test coverage in `e2e/nx/src/run.test.ts` to
verify:
- Projects with a "run" target default to it when no target is specified
- Projects without a "run" target still show the original error message
- Maintains full backward compatibility

## Testing

- All existing tests pass
- Added new e2e tests to verify the behavior
- Ran full validation suite (`nx prepush`) successfully

Author: FrozenPandaz

e2e/nx/src/run.test.ts

@@ -453,6 +453,33 @@ describe('Nx Running Tests', () => {
       );
     }, 10000);
 
+    it('should default to "run" target when only project is specified and it has a run target', () => {
+      const myapp = uniq('app');
+      runCLI(`generate @nx/web:app apps/${myapp}`);
+
+      // Add a "run" target to the project
+      updateJson(`apps/${myapp}/project.json`, (c) => {
+        c.targets['run'] = {
+          command: 'echo Running the app',
+        };
+        return c;
+      });
+
+      // Running with just the project name should default to the "run" target
+      const output = runCLI(`run ${myapp}`);
+      expect(output).toContain('Running the app');
+      expect(output).toContain(`nx run ${myapp}:run`);
+    });
+
+    it('should still require target when project does not have a run target', () => {
+      const myapp = uniq('app');
+      runCLI(`generate @nx/web:app apps/${myapp}`);
+
+      // Project has no "run" target, so it should fail
+      const result = runCLI(`run ${myapp}`, { silenceError: true });
+      expect(result).toContain('Both project and target have to be specified');
+    });
+
     describe('target defaults + executor specifications', () => {
       it('should be able to run targets with unspecified executor given an appropriate targetDefaults entry', () => {
         const target = uniq('target');