feat(client): add STATION_CODE env var and config attribute

Reads STATION_CODE from the environment and exposes it as Config.STATION_CODE
(None when unset or empty). Adds the variable to .env.example with a
per-station deployment note, and covers both read and missing-key paths with
new pytest tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -20,6 +20,10 @@ CLIENT_HOST=0.0.0.0
 CLIENT_PORT=5000
 CLIENT_SECRET_KEY=change-this-to-another-random-secret-key
 API_SERVER_URL=http://localhost:8000
+# Station code this client container belongs to (e.g. ST-001).
+# Each physical tablet/PC deployment must set this unique per-station value.
+# Leave empty only for a single-station all-in-one demo using ST-DEFAULT.
+STATION_CODE=ST-DEFAULT
 
 # --- File Storage ---
 UPLOAD_DIR=server/uploads

client/config.py

@@ -22,6 +22,10 @@ class Config:
     PERMANENT_SESSION_LIFETIME = 28800  # 8 hours
     WTF_CSRF_TIME_LIMIT = 3600  # 1 hour
 
+    # Station identity: each deployed client container sets this to the station
+    # code it belongs to. Empty/None means "not configured".
+    STATION_CODE: str | None = os.getenv("STATION_CODE") or None
+
     # Babel i18n
     BABEL_DEFAULT_LOCALE = "it"
     BABEL_DEFAULT_TIMEZONE = "Europe/Rome"

client/tests/test_config_station.py

@@ -0,0 +1,17 @@
+"""Tests that STATION_CODE is loaded from env and exposed on the client Config class."""
+import importlib
+import os
+
+
+def test_station_code_read_from_env(monkeypatch):
+    monkeypatch.setenv("STATION_CODE", "ST-TEST")
+    import config
+    importlib.reload(config)
+    assert config.Config.STATION_CODE == "ST-TEST"
+
+
+def test_station_code_defaults_to_none_when_missing(monkeypatch):
+    monkeypatch.delenv("STATION_CODE", raising=False)
+    import config
+    importlib.reload(config)
+    assert config.Config.STATION_CODE is None