test: add a local Docker test environment for all features

testenv/ starts two real NetBox 4.7 instances (v2 and v1 token), SSH
targets on public, mgmt, and prod networks, a jump host, an IPv6-only
host, a static host, and a client with ssh, sftp, scp, tmux, zellij,
bash, zsh, and fish. A seed script fills NetBox through the REST API.

141 end-to-end checks cover cache and refresh filters, connecting,
all resolver strategies, multiple instances, shortcuts and rewrites,
SSH options and rules, static hosts, sftp/scp incl. IPv6 and jump
hosts, tunnels, local notes and NetBox comments, completion and shell
hooks, the TUI (driven through tmux), the configurator, and uninstall.

Local only: testenv/up.sh, test.sh, shell.sh, down.sh. Not part of
CI/CD.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

testenv/tests/drive.py

@@ -0,0 +1,32 @@
+"""Drive `netssh configure` in huh's accessible mode (TERM=dumb): one answer
+per prompt, sent after a short pause so each form reads its own line."""
+import os
+import pty
+import select
+import sys
+import time
+
+answers = sys.argv[1:]
+pid, fd = pty.fork()
+if pid == 0:
+    os.execvpe("netssh", ["netssh", "configure"], dict(os.environ, TERM="dumb"))
+out = b""
+
+
+def drain(seconds):
+    global out
+    end = time.time() + seconds
+    while time.time() < end:
+        ready, _, _ = select.select([fd], [], [], 0.05)
+        if ready:
+            try:
+                out += os.read(fd, 4096)
+            except OSError:
+                return
+
+
+for answer in answers:
+    drain(0.5)
+    os.write(fd, (answer + "\n").encode())
+drain(2)
+sys.stdout.write(out.decode(errors="replace"))