doc: split per-host READMEs, gitea cross-repo links, consistency pass

- nuc/README.md and ks4/README.md carry the host sections (+ network
  flows) that lived in the top-level README; links rebased
- top README: repo links (doc/scripts on git.lutran.fr), index points
  at the new per-host pages
- cross-repo references now use https://git.lutran.fr/julien/scripts
  instead of relative ../scripts paths that resolve nowhere
- plakar-s3-data.md and plakar-incus-integration.md marked SUPERSEDED
  / RETIRED with pointers to restic-backup.md; their measurements and
  rationale kept
- install.md, local-backup-cron.md, incus-copy.md: crontab sections
  updated to the live schedule (01:00 replicas, 05:00 restic, Sun
  maintenance); retired legs labelled as such
- restic-backup.md: status live, cutover recorded, post-GC memory
  estimate, seed plan dated
- seafile-gc.md: online GC noted, stale 'crons commented out' removed
- ks2/: what-ks2-does-today rewritten (nothing writes to it any more),
  legs table and gates reflect restic, decommission steps updated
- db-exclude replaces the plakar-era config name (script keeps a
  fallback)

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

ks4/install.md

@@ -142,22 +142,32 @@ All in the `default` project, on the `default` profile
 
 ## Backups
 
-> **Migration in progress** (2026-08-09): the `ks2` destination below is
-> being replaced by a local `backup` zpool on `sdb5` + off-site pull
-> from nuc — plan and setup in [incus-copy.md](incus-copy.md). The
-> cron blocks here describe what runs **today**; update on cutover.
-
-Two **root** cron jobs (this repo's [`scripts/`](../scripts/) are the
-copies that run here) — the primary safety net for the non-mirrored
-`data` pool:
+Full picture, schedule and restore procedures:
+**[../backup-strategy.md](../backup-strategy.md)**. Drivers live in the
+[scripts repo](https://git.lutran.fr/julien/scripts) and are deployed
+to `/root/scripts`. Current **root** cron jobs — the safety net for the
+non-mirrored `data` pool:
 
 ```cron
-0 1 * * * /root/scripts/incus-copy.sh   -d ks2 -m push
-0 4 * * * /root/scripts/incus-backup.sh -d 164.132.173.57 -u rsyncbackup \
-            -i /root/.ssh/id_rsyncbackup -p 2233 \
-            -f /root/scripts/incus-backup.db -s data
+0 1 * * * /root/scripts/incus-copy.sh -p backup -s backup >> /var/log/incus-copy.log 2>&1
+0 5 * * * /root/scripts/restic-backup.sh >> /var/log/restic-backup.log 2>&1
+0 14 * * 0 /root/scripts/restic-maintenance.sh >> /var/log/restic-maintenance.log 2>&1
 ```
 
+- **01:00 `incus-copy.sh`** → replicas of every instance in project
+  `backup` on the sdb5 pool ([incus-copy.md](incus-copy.md),
+  [local-backup-cron.md](local-backup-cron.md)); the S3 instance leg
+  chains here once seeded.
+- **05:00 `restic-backup.sh`** → auto-discovered DB dumps + the data
+  trees listed in
+  [`scripts/restic-paths`](https://git.lutran.fr/julien/scripts/src/branch/main/restic-paths),
+  into the `restic-data` bucket ([restic-backup.md](restic-backup.md)).
+- **Sun 14:00 `restic-maintenance.sh`** → prune + integrity checks.
+
+Historical (retired 2026-08): the `ks2` push and `incus-backup.sh`
+rsync leg, and the plakar data leg
+([plakar-s3-data.md](plakar-s3-data.md)).
+
 - **01:00 — `incus-copy.sh` → `ks2`**: differential `incus copy … \
   --refresh --refresh-exclude-older --mode push` of every *running*
   instance to remote incus host `ks2` (a near-live replica). `ks2` must