The server and the boitier simulator pass set_credentials from MQTT_USERNAME
and MQTT_PASSWORD (a boitier defaults its username to its id, a username
without password is refused instead of going anonymous, the password never
appears in Debug or errors).

aquaserveur --health-check now checks the database (own connection, SELECT 1)
and the age of the last packet received from the broker, kept in an activity
file. The simulator only refreshes /tmp/health while its MQTT session is
established and removes it on disconnection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UH3JcaVWsmFLC6kyEsVL18

@@ -22,3 +23,1 @@
-
-pass() { echo -e "${GREEN}  ✅ PASS${NC} — $1"; ((PASS++)); }
-fail() { echo -e "${RED}  ❌ FAIL${NC} — $1"; ((FAIL++)); }
+pass() { echo -e "${GREEN}  ✅ PASS${NC} — $1"; PASS=$((PASS + 1)); }

@@ -23,2 +23,2 @@
-pass() { echo -e "${GREEN}  ✅ PASS${NC} — $1"; ((PASS++)); }
-fail() { echo -e "${RED}  ❌ FAIL${NC} — $1"; ((FAIL++)); }
+pass() { echo -e "${GREEN}  ✅ PASS${NC} — $1"; PASS=$((PASS + 1)); }
+fail() { echo -e "${RED}  ❌ FAIL${NC} — $1"; FAIL=$((FAIL + 1)); }