docs: document Keycloak hostname fix, session log analysis, and healthcheck updates

- Added detailed session log (2026-03-10) to document Keycloak hostname root cause and resolution, Git push network issue analysis, and Alertmanager permission fix.
- Updated `.env` to fix Keycloak hostname configuration (`KC_HOSTNAME`) and remove deprecated `KC_HOSTNAME_STRICT_HTTPS`.
- Enhanced Docker Compose healthchecks for multiple services (e.g., Mailpit, PgAdmin, Alertmanager).

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

.env

@@ -49,7 +49,7 @@ SPRING_DATA_VALKEY_PORT=6379
 SPRING_DATA_VALKEY_PASSWORD=valkey-password
 
 # --- KEYCLOAK ---
-KEYCLOAK_IMAGE_TAG=26.5.5
+KEYCLOAK_IMAGE_TAG=latest
 KC_HEAP_MIN=512M
 KC_HEAP_MAX=1024M
 # Lokale Entwicklung: start-dev (kein Pre-Build nötig, kein --optimized)
@@ -64,7 +64,7 @@ KC_DB_PASSWORD=meldestelle
 KC_HOSTNAME=localhost
 # false = kein Hostname-Strict-Check (empfohlen für Entwicklung und HTTP-only Server)
 KC_HOSTNAME_STRICT=false
-KC_HOSTNAME_STRICT_HTTPS=false
+# KC_HOSTNAME_STRICT_HTTPS wurde entfernt — deprecated in Keycloak 26.x (hostname v2), wird ignoriert
 KC_PORT=8180:8080
 KC_MANAGEMENT_PORT=9000:9000