fix(wrapper): follow the shell working directory in the wrapper process (#129)

Fixes #124.

Since #78 the shell reports `IRIS_CWD` on `chpwd`, but the wrapper only
passes it to
`spec.SetCWD` for suggestions. Its own working directory never moves, so
tools that
read the pane's foreground process to locate the shell resolve the wrong
path after a
`cd`. I hit this with herdr, which stopped detecting the git repository
of a pane once
IRIS was in it. tmux uses the same lookup for `pane_current_path`.

The absolute path check matches what `spec.SetCWD` already does, so both
treat a
malformed value the same way. The `os.Chdir` error is dropped because
the path comes
from the shell integration, the user cannot act on the failure, and
keeping the last
known directory is better than stopping the loop.

`go test ./...` passes. I tested this end to end on macOS only: the
wrapper followed
the `cd`, and herdr picked the repository back up.

One limitation: the outer launcher process keeps its start directory,
only the wrapper
running `runWrapper` follows. That was enough for herdr, which reads the
wrapper.

root/wrapper.go

@@ -117,6 +117,13 @@ func restoreTerminal() {
 	}
 }
 
+func syncProcessCWD(cwd string) {
+	if !filepath.IsAbs(cwd) {
+		return
+	}
+	_ = os.Chdir(cwd)
+}
+
 // runWrapper sets up the pty environment, launches the shell,
 // and manages the main input loop to provide real-time suggestions
 // it handles raw terminal mode to intercept keystrokes and
@@ -494,6 +501,7 @@ func runWrapper() {
 
 			if cwd, ok := strings.CutPrefix(query, "IRIS_CWD:"); ok {
 				spec.SetCWD(cwd)
+				syncProcessCWD(cwd)
 				continue
 			}