fix(generate): use selected project name for specFileSuffix lookup

[yogeshwaran-c]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

When a user runs nest generate in a monorepo project and is prompted to select a project (because no --project flag was provided), the getSpecFileSuffix call incorrectly uses appName (the original CLI input, which is empty/falsy at this point) instead of selectedProjectName (the project the user just selected from the interactive prompt).

This means that per-project specFileSuffix configuration in nest-cli.json is silently ignored when a project is interactively selected, and the global default is used instead.

Example config where this matters:

{
  "projects": {
    "my-app": {
      "sourceRoot": "apps/my-app/src",
      "generateOptions": {
        "specFileSuffix": "test"
      }
    }
  }
}

Running nest generate service foo and selecting my-app from the prompt would generate foo.spec.ts instead of the expected foo.test.ts.

What is the new behavior?

getSpecFileSuffix now receives selectedProjectName — consistent with the adjacent shouldGenerateSpec and shouldGenerateFlat calls that already correctly use selectedProjectName.

The one-line fix (line 123 of actions/generate.action.ts):

-        appName,
+        selectedProjectName,

Additional context

This bug was introduced in #1968 when the specFileSuffix feature was added. The shouldGenerateSpec and shouldGenerateFlat calls were already using selectedProjectName, but getSpecFileSuffix was mistakenly wired to appName.