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- plakar-s3-data.md and plakar-incus-integration.md marked SUPERSEDED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>

ks2/plan.md

@@ -4,20 +4,23 @@ Goal: release `ks2.lutran.fr` (`164.132.173.57`, SSH :2233, host
 `ns3247221`) once ks4 has a real 3-2-1 backup without it.
 **Deadline: rental ends Sep 30, 2026.**
 
-## What ks2 does today (updated 2026-08-22)
+## What ks2 does today (updated 2026-08-28)
 
-One remaining role, fed nightly by a root cron **on ks4**:
+**Nothing is written to ks2 any more.** Both feeds are retired: the
+`01:00` replica push (replaced by the local leg on ks4's sdb5 pool,
+[local-backup-cron.md](../ks4/local-backup-cron.md)) and the `04:00`
+`incus-backup.sh` rsync (replaced by restic → S3,
+[restic-backup.md](../ks4/restic-backup.md)).
 
-- `04:00` `incus-backup.sh … -d 164.132.173.57` — DB dumps + selected
-  paths rsync'd to ks2 `/backup/ns3061243` on pool `backup` (1.59 T,
-  88 % full), snapshotted daily on ks2 (`zfs-auto-snapshot.sh`,
-  2-month expiry). **Kept as a stopgap** until the plakar S3 leg
-  replaces it.
+What remains on the box is **cold history**: instance replicas on pool
+`data` (last refreshed 2026-08-09) and the rsync tree
+`/backup/ns3061243` on pool `backup` (last refreshed 2026-08-28),
+snapshotted daily there (`zfs-auto-snapshot.sh`, 2-month expiry).
 
-Retired: the `01:00` replica push to ks2 pool `data` — replaced by
-the local leg on ks4's sdb5 pool
-([local-backup-cron.md](../ks4/local-backup-cron.md)); `biwiki` and `spot`
-deleted from ks2.
+⚠️ Consequence while the nuc leg waits for FTTH: **instances have no
+fresh off-site copy** — only the ks4-local sdb replicas plus ks2's
+ageing ones. Either re-enable the interim push (below) or accept the
+gap knowingly until FTTH.
 
 ## Inventory findings (2026-08-22)
 
@@ -25,8 +28,9 @@ deleted from ks2.
   project — **decision: both abandoned**, safe to delete from backups.
 - `incus-backup.db` is stale (lists `spot`, misses `livetrail`,
   `outline`, `login`, …) — forgotten-manifest drift is exactly what
-  the plakar-based replacement must eliminate (back up *all*
-  instances by default, opt-out instead of opt-in).
+  the replacement had to eliminate — restic's drivers back up *all*
+  instances and auto-discover *all* databases, opt-out instead of
+  opt-in.
 - `livetrail` (running on ks4) is **absent from ks4's local `backup`
   project** — the local leg was run manually once and never again;
   automating its cron fixes this.
@@ -38,17 +42,17 @@ deleted from ks2.
   `qcm`) — those instances still exist stopped on ks4, so nothing
   unique expected there; spot-check before wiping.
 - Losing ks2 also loses its 2 months of rsync-snapshot history —
-  acceptable once plakar has built equivalent retention.
+  acceptable: restic keeps 14 daily / 8 weekly / 6 monthly.
 
 ## Target architecture (3-2-1 for ks4)
 
 | Leg | Mechanism | Status |
 |---|---|---|
-| local, 2nd disk | `incus-copy.sh -p backup -s backup` → sdb5 pool | works, **cron missing** |
-| off-site, nuc | nuc pulls `ks4:*` → pool `ks4backup` over WG | waiting FTTH seed |
-| off-site, S3 (data+DB) | **restic** on ks4 → S3 (plakar ran it first, being replaced — see [restic-backup.md](../ks4/restic-backup.md)) | migrating |
-| off-site, S3 (instances) | restic over `incus file mount` of the `backup`-project replicas | designed |
-| off-site, ks2 (interim) | 02:00 replica push until the nuc leg seeds (FTTH < Sep 30) | to re-enable |
+| local, 2nd disk | `incus-copy.sh -p backup -s backup` → sdb5 pool | **live** (01:00) |
+| off-site, S3 (data+DB) | **restic** → bucket `restic-data` ([restic-backup.md](../ks4/restic-backup.md)) | **live** (05:00) |
+| off-site, S3 (instances) | restic over `incus file mount` of the `backup`-project replicas | written, **not seeded** |
+| off-site, nuc | nuc pulls `ks4:*` → pool `ks4backup` over WG ([nuc-seed.md](nuc-seed.md)) | waiting FTTH (< Sep 30) |
+| off-site, ks2 (optional interim) | `incus-copy.sh -d ks2 -m push` at 02:00 until the nuc leg seeds | **not enabled** — decide |
 
 ## Actions (backup work documented in [`../ks4/`](../ks4/), ks2-only tasks here)
 
@@ -57,13 +61,11 @@ deleted from ks2.
 2. ~~[local-backup-cron.md](../ks4/local-backup-cron.md)~~ — **done
    2026-08-22**: leg 1 cron re-enabled, ks2 rsync kept as stopgap;
    `livetrail` verified present in the `backup` project
-3. [plakar-s3-data.md](../ks4/plakar-s3-data.md) — **seeding S3
-   2026-08-22** (direct-to-S3 kloset `lutran-ks4-plakar-data`, driver
-   script `scripts/plakar-backup.sh`, pipeline validated locally);
-   next: restore test + cron
-4. [plakar-incus-integration.md](../ks4/plakar-incus-integration.md) —
-   design seeded 2026-08-22: per-file importer over the incus sftp
-   API, instances → S3
+3. ~~plakar S3 leg~~ → **replaced by restic**
+   ([restic-backup.md](../ks4/restic-backup.md), live 2026-08-28;
+   plakar's own doc kept as history)
+4. instance leg — restic over `incus file mount`
+   ([restic-backup.md](../ks4/restic-backup.md) §6): **seed pending**
 5. [nuc-seed.md](nuc-seed.md) — **prepared**; after FTTH: seed nuc
    pull leg, verify all instances, test-restore one
 6. [decommission.md](decommission.md) — **prepared**; cut flows,
@@ -74,6 +76,6 @@ deleted from ks2.
 - [x] biwiki + spot consciously abandoned (2026-08-22)
 - [ ] local leg cron running ≥ a few days, all instances present
 - [ ] nuc leg fully seeded **and** one instance test-restored
-- [ ] plakar S3 data/DB backups running daily **and** one DB + one
+- [ ] restic S3 data/DB backups running daily **and** one DB + one
       file tree test-restored
 - [ ] ks4 crons pointing at ks2 disabled