docs: distill the retired workstation's KB pages into general pages

Frank's call: no per-host graveyard. The four /system/dankware/ pages carried
two pieces of knowledge that outlive the box, and one that does not.

Distilled:
- omp-docs/system/network.md (new) — LAN topology plus the multi-link resolver
  law: a client with two +DefaultRoute links flaps its DNS, and the fix is a
  static per-connection resolver, not resolved.conf. Keeps the
  flush-caches-loop verification, because one successful dig proves nothing.
- omp-docs/tools/niri/displays.md (new) — the multi-monitor rig: portrait
  transforms, absolute positions, auto-placed third panel, the iGPU
  render-node pin, and the three failure modes (duplicate output blocks,
  positions that do not reflow, a mode the panel cannot drive).

Dropped: the machine's own spec sheet (CPU/GPU/PCI/NVMe inventory for a box
Frank sold) and its quick-facts table. The OS and userspace facts it repeated
already live in tools/cachyos.md.

omp-docs/system/dankware/ moved to .AGENTTRASH/20260928-retired-workstation/
(not deleted; git history holds it too). system/index.md and the niri index
repoint; niri's [[displays]] wikilink now resolves to the new page instead of
the trashed one. kb-lint: 0 violations.

omp-docs/tools/niri/index.md

@@ -85,11 +85,12 @@ Column-based scrollable tiling. Columns are cycled with Mod+Left/Right (or Mod+H
 | [[default-bindings|default-bindings.md]] | reference | Default key bindings organized by category |
 | [[key-bindings-syntax|key-bindings-syntax.md]] | reference | KDL configuration syntax for key bindings |
 | [[tips|tips.md]] | howto | Practical tips for working with niri |
+| [[displays|displays.md]] | reference | Multi-monitor display rig: portrait transforms, positions, scale, iGPU display ownership |
 
 ---
 
 ## See Also
 
 - [[noctalia-shell|noctalia-shell]] — Desktop shell integration
-- [[displays|displays]] — Three-monitor setup
+- [[displays|displays]] — Multi-monitor desk rig configuration
 - [[cachyos|cachyos]] — Operating system