fix: updated string that identifies escape key presses when prompting for required vars

[anilnatha]

This PR addresses a fix needed to identify if the escape key is pressed when a user is prompted for a required variable.

The issue existed in internal/input/input.go where there were two switch statements that checked if the escape key was pressed using the string escape. However, uv identifies the escape key using the string esc, not escape. Because of this discrepancy, task never quit when the escape key was pressed after prompting the user for a required var. After changing escape to esc and running the following two tests I was able to verify that the issue has been fixed:

go run ./cmd/task --dir ./testdata/interactive_vars deploy
go run ./cmd/task --dir ./testdata/interactive_vars release

AI Disclosure: I used Cursor to help me identify where in the code the keypress events were being done when prompting for required vars. I then investigated the uv and bubbletea documentation and codebases to identify that the escape key string may have been incorrect. Then experimented on my macOS system (v26.5.2), swapping between the strings escape and esc at the locations identified in the changed files and running the two tests above a number of times.

• I have read and followed the Contribution Guide

[anilnatha]

Hello, this is my first PR for this codebase.

While I have tested this change using the listed tests above, being new to this codebase I wanted to ask if I should have left the original string for escape alongside the string esc for any compatibility reasons.