The image creates SWW_STATE_DIR when it is missing (closes #337)

Before `waf` starts, the image's `run` script now makes `SWW_STATE_DIR` if it is missing (`mkdir -p`), gives it to `sww:sww` and sets its mode to `0700`, as it already does for the cache directory's owner. A value that is not an absolute path, or an unreadable `SWW_STATE_DIR_FILE`, still changes nothing, and `waf` stops naming the setting. The `Dockerfile` comment, `docs/image.md`, `docs/settings.md` and `SPEC.md` say the image makes the directory. `script/example-app` checks that a missing `SWW_STATE_DIR` is made, owned by `sww` with mode `0700`.

- `chmod 0700` also applies to an existing directory, a mounted volume included, at every start of `waf`.

Model: opus-5-5

Dockerfile

@@ -222,8 +222,8 @@ RUN groupadd --system --gid 65532 sww \
         sww
 
 # The state files' directory, SWW_STATE_DIR by default, where a volume
-# is mounted to keep them across deploys. The run script gives it to the
-# sww user at each start of waf.
+# is mounted to keep them across deploys. At each start of waf, the run
+# script makes SWW_STATE_DIR if it is missing and gives it to the sww user.
 RUN mkdir /var/lib/sww
 
 # The default rule file, in SWW_RULES_DIR by default, where a Dockerfile