release: 2.10.4: origin-strict - a change with neither header is refused

Cut without asking, as the owner said on 2026-10-15. A POST with neither
Sec-Fetch-Site nor Origin is refused (the commit before this); the e2e
client sends Origin. go vet, go test (26 packages) and make e2e passed on
the test server for that tree. No migration, schema 12.

CHANGELOG [2.10.4]; pins in deploy/docker-compose.yml, README and the guide
(pin, build, the sample restore message); development's "from pin" and
row 36; roadmap row. No tag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/guide.md

@@ -204,14 +204,14 @@ cat ./data/setup-token
 #### Fixed image tag
 
 `deploy/docker-compose.yml` pins an explicit version (`ghcr.io/mixeme/selfpost:X.Y.Z`),
-deliberately never `:latest`. The current pin is `2.10.3`. **No 2.x image is
+deliberately never `:latest`. The current pin is `2.10.4`. **No 2.x image is
 published on ghcr.io yet** (the newest there is `1.3.0`); until one is, build
 it from the checkout under the pinned name, and Compose uses the local image
 instead of pulling:
 
 ```sh
-docker build -f build/Dockerfile --build-arg VERSION=2.10.3 \
-  -t ghcr.io/mixeme/selfpost:2.10.3 .
+docker build -f build/Dockerfile --build-arg VERSION=2.10.4 \
+  -t ghcr.io/mixeme/selfpost:2.10.4 .
 ```
 
 `VERSION` must equal the tag: it is the version the backup check compares
@@ -953,7 +953,7 @@ A version mismatch at step 5 refuses to start and leaves `/data` untouched —
 the panel exits with a message naming the tag to use, e.g.:
 
 ```
-backup: this backup was created by SelfPost 2.10.2 but this image is 2.10.3 — restore into the matching image (selfpost:2.10.2)
+backup: this backup was created by SelfPost 2.10.3 but this image is 2.10.4 — restore into the matching image (selfpost:2.10.3)
 ```
 
 Fix the tag in `docker-compose.yml` (build that tag as under [Fixed image