[FEATURE] Allow user stdin passthrough for interactive Bash commands

Description

When Claude Code's Bash tool runs a command that requires interactive input (password prompts, y/n confirmations, interactive installers), there's currently no way for the user to provide stdin. The command either hangs until timeout or fails.

Use Case

The most common case: a command requires sudo and prompts for a password. Currently the only workarounds are:

• Pre-running sudo -v before the session
• Using --noconfirm / --yes flags (not always available)
• Piping input via echo (doesn't work for passwords, insecure)

Proposed Solution

Allow the user to "attach" to the running Bash process's TTY to provide interactive input when needed. Similar to how GeminiCLI handles this — the user can tab into the terminal and type directly when a command is waiting for input.

Current Behavior

Command needing stdin → hangs → times out → fails

Expected Behavior

Command needing stdin → user is notified → user can type into the process → command completes → Claude sees output

Environment

• Platform: Linux (Arch)
• Shell: fish
• Claude Code: latest