feat(console): manage 7 switch consoles via ser2net+conman on pfv-tsys4

Solve the long-standing USB adapter enumeration shift problem: 9 Prolific
USB-to-DB9 adapters on pfv-tsys4 have no unique serial numbers and get
assigned /dev/ttyUSB0-8 based on enumeration order, which changes on every
reboot and breaks the old /root/conmap + manual screen workflow.

Solution: udev rules pin each adapter by its ID_PATH (physical USB port
topology), which is stable across reboots regardless of enumeration order.
Each adapter gets a named symlink in /dev/consoles/<name>. ser2net opens
these stable symlinks and exposes them on TCP ports (2001-2007) bound to
the Tailscale interface only. conman connects to those TCP ports for
session logging and multi-user console sharing.

Architecture (layered, no port sharing):
  USB adapter → udev symlink → ser2net (TCP) → conman (logging + mux)

Port assignments (all on Tailscale IP 100.70.77.93):
  2001 = pfv-core-sw01     2002 = pfv-tor3-mgmt    2003 = pfv-tor3-stor
  2004 = pfv-rrinfra-rtr   2005 = pfv-r2-tor-top   2006 = subodev-torsw
  2007 = pfv-r2-sw

Scripts (console/):
- mapping.txt: source of truth (TCP port | name | ID_PATH | baud | comment)
- generate-config.sh: generates udev rules, ser2net.yaml, conman.conf
  entries from mapping.txt. Idempotent (markers in conman.conf for clean
  regeneration). Uses | delimiter (ID_PATH values contain colons).
- setup.sh: full deploy — generate configs, create symlinks (udev trigger
  + manual fallback for already-discovered devices), create conmand
  systemd unit (Debian doesn't ship one), restart services
- discover.sh: read-only USB adapter and service state discovery
- validate-conman.sh: verify conman→ser2net→device data path and log capture

Issues fixed during development:
- /dev/console is a kernel char device (major 5, minor 1) — cannot create
  a directory there. Changed symlink namespace to /dev/consoles/.
- conman 0.3.x has no 'include' directive — CONSOLE entries written
  directly into /etc/conman.conf between idempotent markers.
- Debian conman package has no systemd unit — created
  /etc/systemd/system/conmand.service with After=ser2net ordering.
- conman.conf had no LOGDIR — logs weren't being written to
  /var/log/conman/. Fixed by adding server logdir directive.

Validation: 7 symlinks resolving, 7 TCP ports on Tailscale, conmand with
7 consoles registered, 7 log files actively capturing console output,
both services enabled for reboot survival.

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

docs/docmap.md

@@ -43,6 +43,7 @@ Server provisioning, security hardening, DNS/NTP configuration.
 | Document | Description | Last Reviewed |
 |----------|-------------|---------------|
 | [`../powerman/README.md`](../powerman/README.md) | Cyclades PM10i PDU management via powerman on pfv-tsys1 | 2026-07-28 |
+| [`../console/README.md`](../console/README.md) | Serial console management (ser2net + conman) for 7 network switches on pfv-tsys4 | 2026-07-28 |
 | [`../k8s/README.md`](../k8s/README.md) | k3s cluster setup scripts: wipe, bootstrap, taint, verify (3-node HA over Tailscale) | 2026-07-28 |
 | [`../dns-cluster-setup/README.md`](../dns-cluster-setup/README.md) | Technitium DNS cluster setup: export, deploy, cluster, verify | 2026-07-28 |
 | [`../tests/README.md`](../tests/README.md) | Test suite documentation: unit, security, validation tests | 2026-07-28 |