fix: stdin handling and exit command (#58)

### Summary of Changes
Fixes **#53** (*Fish shell integration panics with `inappropriate ioctl
for device`*).
#### 1. Fixed Non-TTY Stdin (`panic: inappropriate ioctl for device`) —
Fixes #53
- **Root Cause**: When executing `iris init fish | source` (or sourcing
shell configs), `os.Stdin` (FD 0) is connected to a pipe instead of a
TTY. Calling `term.MakeRaw()` on
a pipe returns `ENOTTY`.
- **Fix**: Guarded `term.MakeRaw()` with `term.IsTerminal()` checks
across `root/wrapper.go` and `root/root.go`. Added fallback to open and
use `/dev/tty` when `os.Stdin` is
  not a terminal device.
- **Fish IPC Hooks**: Added `fish_preexec` and `fish_postexec` event
handlers to `iris init fish` to send `IRIS_CMD_START` / `IRIS_CMD_STOP`
IPC signals over `$IRIS_FD`.
  
#### 2. Fixed Shell Setup Order (Duplicate `fastfetch` / startup
executions) — Fixes #53
- **Root Cause**: `iris setup` appended the init script to the bottom of
shell configs (`config.fish`, `.zshrc`, `.bashrc`), causing pre-existing
interactive startup commands
  to run twice.
- **Fix**: Updated `setupCmd` in `root/init.go` to **prepend** `# Iris
Autocomplete` to the top of shell configuration files.
  
#### 3. Fixed Terminal Exit Loop Handling — Relates to #50
- **Root Cause**: When typing `exit` in the wrapped shell, Linux PTY
returns `syscall.EIO` (`Input/output error`) on `ptmx.Read()` rather
than `io.EOF`. `runWrapper()` was
ignoring non-EOF errors and looping indefinitely without restoring the
terminal or calling `os.Exit(0)`.
- **Fix**: Updated the `ptmx.Read` error handler in `root/wrapper.go` to
handle `syscall.EIO` and exit cleanly.
  
   ---
  
  ### Issues Addressed
   - Closes #53
   - Relates to #50, #55
  
   ---
  
  ### Verification Tested
- [x] Verified `iris setup fish` / `iris init fish | source` initializes
without `ioctl` panic.
- [x] Verified typing `exit` in Fish, Zsh, and Bash terminates IRIS
cleanly and restores standard terminal state.
   - [x] Ran `go test ./...` — all tests pass.

---------

Co-authored-by: verse91 <versedev.store@proton.me>
Co-authored-by: VERSE <sunnyone0901@gmail.com>

root/crash.go

@@ -20,7 +20,8 @@ func startRescueShell() {
 	if shell == "" {
 		shell = "/bin/sh"
 	}
-	_ = syscall.Exec(shell, []string{shell}, os.Environ())
+	env := append(os.Environ(), "IRIS_RESCUE=1")
+	_ = syscall.Exec(shell, []string{shell}, env)
 }
 
 var (