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- plakar-s3-data.md and plakar-incus-integration.md marked SUPERSEDED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/restic-backup.md

@@ -1,10 +1,12 @@
 # restic backups on ks4 — the S3 leg
 
-Status: **decided 2026-08-25 — restic replaces plakar as the S3
-backup tool** (evaluation first: parallel run + comparison, see §8).
-Final architecture: **two tools** — `incus copy` for replication
-(local sdb, nuc after FTTH, ks2 push as interim), **restic** for
-everything S3.
+Status: **live since 2026-08-28** — restic replaced plakar as the S3
+backup tool (plakar crons off, its kloset kept for
+[#2338](https://github.com/PlakarKorp/plakar/issues/2338); see §8).
+Architecture: **two tools** — `incus copy` for replication (local sdb,
+nuc after FTTH), **restic** for everything S3. Data leg (`restic-data`)
+runs nightly at 05:00; the instance leg (`restic-incus`, §6) is written
+and awaits its first seed.
 
 Why: plakar's incremental cost scales with tree size, not churn
 (~800 MiB parent metadata re-read from S3 + hours of CPU per night on
@@ -58,9 +60,10 @@ property).
 ### Memory (the real constraint on this 23/31 GiB-used box)
 
 - Index RAM ≈ 200–300 B/blob → combined `restic-data` index
-  ~1–1.5 GiB per operation (nextcloud ~1 M blobs + seafile ~2–4 M);
-  prune peaks 2–3×. Accepted with the merged layout (§1) — measure
-  peak RSS during the evaluation week (`/usr/bin/time -v`).
+  ~1 GiB per operation; prune peaks 2–3×. The seafile side of that
+  estimate collapsed after its garbage collection (24.9 M → 0.5 M
+  objects, [seafile-gc.md](seafile-gc.md)). Measure peak RSS with
+  `/usr/bin/time -v` if the box ever feels tight.
 - `GOGC=20` trades CPU for a smaller Go heap — enable if the seafile
   prune ever pressures the box.
 
@@ -140,7 +143,7 @@ for r in restic-data restic-incus; do
 done
 ```
 
-## 4. Seed plan
+## 4. Seed plan (executed 2026-08-25 → 08-28)
 
 1. **ARC floor first** (helps every walk on the box):
    ```sh
@@ -252,18 +255,18 @@ restic -r s3:…/restic-data restore latest --target /backup/restore-test --incl
 diff -r … && rm -rf /backup/restore-test
 ```
 
-## 8. Evaluation protocol + plakar retirement
+## 8. Cutover (done) + what is left
 
-- **Parallel week**: plakar 04:30 cron keeps running untouched;
-  restic runs at 05:00 on the same data. Same nights, same churn →
-  direct comparison (wall, bytes read from store, bytes written, peak
-  RSS via `/usr/bin/time -v`) against plakar's measured table in
-  [plakar-s3-data.md](plakar-s3-data.md). Restore-speed compared on
-  the same 10 GiB dumps tree (plakar measured: 39 min).
-- **Cutover** (after the comparison confirms + restore test passes):
-  drop the plakar 04:30 + Sunday-check crons; 01:00 becomes
-  `incus-copy ; restic instances phase` (or stays in the 05:00 run).
-  Update plan.md legs table.
+- **Cutover 2026-08-28**: plakar's 04:30 and Sunday crons are off;
+  restic's 05:00 data leg is the S3 backup. The formal parallel-week
+  comparison was cut short — the evidence had already settled it
+  (plakar: ~800 MiB metadata re-read and 3–4 h per night on the
+  nextcloud tree, churn-independent; restic: seed at 60–115 MiB/s,
+  local-cache incrementals). plakar's measurements stay in
+  [plakar-s3-data.md](plakar-s3-data.md).
+- **Left to do**: seed `restic-incus` (§6) and chain it onto the 01:00
+  line; restore test on the complete `restic-data`; then the ks2
+  decommission gates ([../ks2/plan.md](../ks2/plan.md)).
 - **plakar retirement, one exception**: keep plakar installed and
   keep the `plakar-data` kloset until
   [#2338](https://github.com/PlakarKorp/plakar/issues/2338) concludes