release: 2.15.0: server-dmarc-hint, upstream-tls-verify

The server's own name gets a DMARC record on Settings and Health, and an
inbound domain's upstream a Verified TLS mode (Postfix secure, with
Debian's CA bundle). Migration 0014; schema 14. The pins (compose, README,
guide), the guide's backup example, the planned cuts and the two roadmap
rows. No tag.

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

docs/guide.md

@@ -218,14 +218,14 @@ 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 `2.14.5`. **No 2.x image is
+deliberately never `:latest`. The current pin is `2.15.0`. **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=2.14.5 \
-  -t ghcr.io/mixeme/selfpost:2.14.5 .
+docker build -f build/Dockerfile --build-arg VERSION=2.15.0 \
+  -t ghcr.io/mixeme/selfpost:2.15.0 .
 ```
 
 `VERSION` must equal the tag: it is the version the backup check compares
@@ -1073,7 +1073,7 @@ 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 2.14.4 but this image is 2.14.5 — restore into the matching image (selfpost:2.14.4)
+backup: this backup was created by SelfPost 2.14.5 but this image is 2.15.0 — restore into the matching image (selfpost:2.14.5)
 ```
 
 Fix the tag in `docker-compose.yml` (build that tag as under [Fixed image