fix: sync shell working directory for suggestions (#78)

## Summary
- synchronize the shell current working directory with Iris over the
existing IPC pipe
- use the synchronized directory for file, workspace, Git, and history
suggestions on macOS
- preserve the Linux `/proc/<pid>/cwd` and process-CWD fallbacks
- update zsh, bash, and fish integrations while preserving command exit
status

## Problem
On macOS, `/proc/<pid>/cwd` is unavailable, so `GetCWD` fell back to the
directory where Iris was launched, usually `$HOME`. After changing
directories in the shell, file suggestions could therefore continue to
come from `$HOME`.

## Tests
- `go test -race ./spec`
- `go test ./root -run ^'$'`
- `go test ./... -run ^'$'`
- generated zsh, bash, and fish hook syntax checks

Co-authored-by: Pavel Naumov <Pavel.Naumov@berekebank.kz>

root/wrapper.go

@@ -386,6 +386,11 @@ func runWrapper() {
 		for scanner.Scan() {
 			query := scanner.Text()
 
+			if cwd, ok := strings.CutPrefix(query, "IRIS_CWD:"); ok {
+				spec.SetCWD(cwd)
+				continue
+			}
+
 			if query == "IRIS_CMD_START" {
 				isCommandActive.Store(true)
 				bufferMu.Lock()