chore: remove local images in make clean, add build target

clean now removes the locally-built backend image (bangui-dev_backend)
in addition to volumes, so the next 'make up' rebuilds from scratch
ensuring code changes land in the new image.
Public images (fail2ban, node:22-alpine) are left untouched.
Added standalone 'make build' target for explicit rebuilds.

Makefile

@@ -7,7 +7,8 @@
 #  Usage:
 #    make up        — start the debug stack
 #    make down      — stop the debug stack
-#    make clean     — stop and remove all debug containers AND volumes
+#    make build     — (re)build the backend image without starting
+#    make clean     — stop, remove all containers, volumes, and local images
 #    make logs      — tail logs for all debug services
 #    make restart   — restart the debug stack
 # ──────────────────────────────────────────────────────────────
@@ -25,6 +26,11 @@ DEV_VOLUMES := \
 	$(PROJECT)_fail2ban-dev-config \
 	$(PROJECT)_fail2ban-dev-run
 
+# Locally-built images (compose project name + service name).
+# Public images (fail2ban, node) are intentionally excluded.
+DEV_IMAGES := \
+	$(PROJECT)_backend
+
 # Detect available compose binary.
 COMPOSE := $(shell command -v podman-compose 2>/dev/null \
              || echo "podman compose")
@@ -32,7 +38,7 @@ COMPOSE := $(shell command -v podman-compose 2>/dev/null \
 # Detect available container runtime (podman or docker).
 RUNTIME := $(shell command -v podman 2>/dev/null || echo "docker")
 
-.PHONY: up down restart logs clean
+.PHONY: up down build restart logs clean
 
 ## Start the debug stack (detached).
 up:
@@ -42,6 +48,10 @@ up:
 down:
 	$(COMPOSE) -f $(COMPOSE_FILE) down
 
+## (Re)build the backend image without starting containers.
+build:
+	$(COMPOSE) -f $(COMPOSE_FILE) build
+
 ## Restart the debug stack.
 restart: down up
 
@@ -49,9 +59,10 @@ restart: down up
 logs:
 	$(COMPOSE) -f $(COMPOSE_FILE) logs -f
 
-## Stop containers and remove ALL debug volumes (database, node_modules, fail2ban data).
-## This returns the environment to a clean first-run state.
+## Stop containers, remove ALL debug volumes and locally-built images.
+## The next 'make up' will rebuild images from scratch and start fresh.
 clean:
 	$(COMPOSE) -f $(COMPOSE_FILE) down --remove-orphans
 	$(RUNTIME) volume rm $(DEV_VOLUMES) 2>/dev/null || true
-	@echo "All debug volumes removed. Run 'make up' to start fresh."
+	$(RUNTIME) rmi $(DEV_IMAGES) 2>/dev/null || true
+	@echo "All debug volumes and local images removed. Run 'make up' to rebuild and start fresh."