feat: replace SFTP drop with Syncthing share path

Remove SFTPGo; mount event data from the Syncthing folder, watch
incoming/, and name variants after the source stem.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -1,21 +1,11 @@
 # Copy to `.env` and fill in real values. Never commit `.env`.
 
-# --- SFTPGo credentials -----------------------------------------------
-# Whoever runs the event camera/laptop uploads photos here.
-SFTP_USER=livef12
-SFTP_PASSWORD=changeme
-
-# --- Host paths / ports --------------------------------------------------
-# On the server this should be an absolute path, e.g.
-# /home/frank/live.f12.rocks/data
-DATA_HOST_DIR=./data
-
-# Spec asked for 121212 which exceeds TCP max (65535). Use 12121.
-SFTP_HOST_PORT=12121
-
-# Minutes until SFTPGo closes an idle connection. Android/SSHJ clients
-# often sit idle after upload; the default 15m shows up as a spurious EOF.
-SFTPGO_IDLE_TIMEOUT=120
+# --- Host data path (Syncthing share root) ------------------------------
+# Prod default (compose.yml): /home/frank/sync.schwenk.online/data/livef12
+# Layout under that path: incoming/  jobs/  processed.json
+# Local override when the absolute path does not exist:
+# DATA_HOST_DIR=./data
+# DATA_HOST_DIR=/home/frank/sync.schwenk.online/data/livef12
 
 # --- Pipeline tuning (see make_random.py for background) -----------------
 OUTPUT_COUNT=3