Fix Dockerfile conflict markers broken on main (#3)

* Fix conflict markers on main and guard CI against them

PR #2 merged before the Dockerfile cleanup landed, leaving <<<<<<<
markers that break docker compose build. Restore clean Docker files
and fail CI if conflict markers appear in the tree.

* Add CI check that fails on merge conflict markers

* Narrow conflict-marker CI check to <<<<<<< and >>>>>>>

---------

Co-authored-by: Cursor Agent <[email protected]>

README.md

@@ -86,7 +86,6 @@ GitHub Actions runs lint, typecheck, and tests on every pull request and push to
 
 ## Docker
 
-<<<<<<< HEAD
 ### docker compose (recommended)
 
 ```bash
@@ -117,26 +116,16 @@ docker compose down
 
 ### Plain docker
 
-=======
->>>>>>> origin/main
 ```bash
 docker build -t rfid-database .
 docker run --rm -p 3000:3000 \
   -e AUTH_SECRET=your-long-secret \
-<<<<<<< HEAD
   -e CREATE_USER_EMAIL=[email protected] \
   -e CREATE_USER_PASSWORD=changeme \
-=======
->>>>>>> origin/main
   -v rfid-data:/data \
   rfid-database
 ```
 
-<<<<<<< HEAD
-=======
-Create the first user against the mounted DB (exec into the container or run `create-user` with `RFID_DB_PATH` pointed at the volume).
-
->>>>>>> origin/main
 ## Security
 
 Tag dumps often include sector keys. Keep the app behind HTTPS, do not expose it publicly without auth, and treat `data/rfid.db` as sensitive.