Keep the database in ./data and bind-mount it

SQLite writes three files — the database plus its -wal and -shm companions.
Putting them in one directory means a deployment mounts a single path and a
backup copies a single directory.

- FOODSTER_DB defaults to ./data/foodster.db, and openDB creates the parent
  directory on startup rather than failing on a fresh checkout
- compose bind-mounts ./data instead of using a named volume, so the file can
  be listed, copied and opened with any sqlite client without going through
  the container engine
- the image runs as UID 65534, which cannot write to a host directory owned
  by someone else, so compose now sets user: from FOODSTER_UID/FOODSTER_GID
- `make up` creates ./data first: left to the engine it appears root-owned
  and the app silently cannot write to it

.env.example

@@ -11,6 +11,12 @@ FOODSTER_PASSWORD=changeme
 # Host port to publish on.
 FOODSTER_PORT=8080
 
+# The database lives in ./data, bind-mounted into the container. These must
+# match whoever owns that directory on the host, or the container cannot
+# write to it. `id -u` and `id -g` will tell you.
+FOODSTER_UID=1000
+FOODSTER_GID=1000
+
 # Used for every calendar-day calculation. Set it in development too: under
 # UTC the date rolls over three hours late, which is exactly when dinner
 # gets logged.