Document the ks2 decommission plan and the new ks4 backup legs

- ks2/: decommission plan with release gates (rental ends Sep 30),
  nuc-seed and final-decommission runbooks
- ks4/local-backup-cron.md: leg-1 cron re-enabled, ks2 rsync stopgap,
  full-resend caveat when refreshes lapse past snapshots.expiry
- ks4/plakar-s3-data.md: plakar direct-to-S3 leg (auto-discovered DB
  dumps incl. grants/globals, fs sources, exclude list, restore test)
- ks4/plakar-incus-integration.md: design + scaffold status of the
  plakar incus importer
- README.md: index ks2/, update the ks4 durability bullet

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -4,6 +4,11 @@ Personal infrastructure notes.
 
 - [`nuc/`](nuc/) — home lab on `nuc` (see below)
 - [`ks4/`](ks4/) — prod server `ks4` at OVH (see below)
+- [`ks2/`](ks2/) — legacy backup server being decommissioned
+  (rental ends Sep 30, 2026): [plan](ks2/plan.md)
+- [`archer-c7/`](archer-c7/) — home router (TP-Link Archer C7 v5,
+  OpenWrt, `192.168.0.2`, WAN = phone USB tether):
+  [upgrade to 25.12](archer-c7/upgrade-openwrt-25.12.md)
 
 ## Homelab: nuc
 
@@ -56,10 +61,15 @@ Incus host at OVH — public-facing self-hosted services.
   outline, login (SSO), wireguard, + more — full table in
   [ks4/install.md](ks4/install.md).
 - ⚠️ The ZFS `data` pool is single-disk (not mirrored); durability
-  rests on two nightly root cron jobs — `incus copy --refresh` to remote
-  host `ks2` (moving to nuc pool `ks4backup`, see
-  [ks4/incus-copy.md](ks4/incus-copy.md)), and an rsync backup
-  (`scripts/incus-backup.sh`) to `164.132.173.57:/backup/ks4`.
+  rests on nightly root cron jobs — 01:00 `incus copy --refresh` of
+  all instances to the local `backup` pool on sdb5
+  ([ks4/local-backup-cron.md](ks4/local-backup-cron.md),
+  [ks4/incus-copy.md](ks4/incus-copy.md)), 04:30 plakar backups
+  (DB dumps + data trees) to S3
+  ([ks4/plakar-s3-data.md](ks4/plakar-s3-data.md)), plus during the
+  transition a 04:00 rsync stopgap to ks2
+  ([ks2 decommission plan](ks2/plan.md)); a pull leg to nuc pool
+  `ks4backup` awaits FTTH.
 
 ## Network flows (nuc <-> ks4)