Add @file tagging in interactive prompts, e.g. plan mode's "Suggest changes" input

### Describe the feature or problem you'd like to solve

In interactive prompts, add the ability to reference files/directories in the same manner as regular prompts.

### Proposed solution

Provides a more consistent workflow for users.
Reduces utilize context by reducing the need for "Search" tool usage (assuming @ tagging does not require the agent to search for the reference)

### Example prompts or workflows

_No response_

### Additional context

_No response_

The issue provides no file or test locations. Start by locating the interactive prompt implementation and the plan mode “Suggest changes” input, then trace how regular prompts handle @ file and directory references. Done means those interactive prompts support equivalent references without requiring the user to search manually.

Scritto dal modello di indicizzazione a partire dal testo della issue.