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/02-connect.sh

@@ -0,0 +1,29 @@
+# Connecting with the resolved address, default user and port, overrides.
+config <<'EOF'
+resolver:
+  strategies: [management_subnet, primary_ip]
+  management_subnets: [10.231.1.0/24]
+ssh:
+  default_user: ops
+EOF
+
+expect_eq "connect via NetBox" "fsn1-pve1" netssh fsn/fsn1-pve1.hoster.test hostname
+expect_eq "unique name without instance" "fsn1-pve2" netssh fsn1-pve2.hoster.test hostname
+expect_eq "default user" "ops" netssh fsn/fsn1-pve1.hoster.test whoami
+expect_eq "user@ wins" "admin" netssh admin@fsn/fsn1-pve1.hoster.test whoami
+expect_eq "-l wins" "admin" netssh -l admin fsn/fsn1-pve1.hoster.test whoami
+expect_eq "remote command with arguments" "a b" netssh fsn/fsn1-pve1.hoster.test echo a b
+expect_eq "dry run" "ssh -l ops 10.231.1.11" netssh --dry-run fsn/fsn1-pve1.hoster.test
+
+config <<'EOF'
+resolver:
+  strategies: [management_subnet, primary_ip]
+  management_subnets: [10.231.1.0/24]
+ssh:
+  default_user: ops
+  default_port: 2222
+EOF
+expect_out "default port" " 2222" netssh fsn/fsn1-pve1.hoster.test 'echo $SSH_CONNECTION'
+expect_out "-p wins over default port" " 22" netssh -p 22 fsn/fsn1-pve1.hoster.test 'echo $SSH_CONNECTION'
+expect_eq "dry run with port" "ssh -p 2222 -l ops 10.231.1.11" netssh --dry-run fsn/fsn1-pve1.hoster.test
+expect_eq "version" "netssh" bash -c 'netssh --version | cut -d" " -f1'