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

.gitignore

@@ -7,7 +7,8 @@
 # Generated by `templ generate` during the container build.
 *_templ.go
 
-# Local database
+# The database and its SQLite companions.
+/data/
 *.db
 *.db-shm
 *.db-wal