Shell mode input placeholder suggests chat features but only accepts shell commands

[JayadityaGit]

When entering shell mode, the input placeholder continues to suggest normal chat usage, but the input only accepts shell commands.

As a result, regular messages and @ file path references fail, even though the UI implies they should work. This mismatch can confuse users when switching to shell mode.

Expected: The placeholder should clearly indicate that only shell commands are supported in shell mode.