v0.27.3: Use real system memory everywhere, add monitoring memory bar

Deploy page, pre-start check, and deploy validation now use actual
/proc/meminfo usage instead of declared mem_request sums. New
GetMemoryMB() helper for lightweight real-time memory reads. Monitoring
page gains a stacked memory distribution bar showing per-container
usage, OS overhead, and free memory.

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

controller/internal/stacks/deploy.go

@@ -123,33 +123,33 @@ func (m *Manager) DeployStack(req DeployRequest) (string, error) {
 	// --- Memory validation ---
 	var deployWarning string
 	reservedMB := m.cfg.System.ReservedMemoryMB
-	totalMB, memErr := system.GetTotalMemoryMB()
+	totalMB, usedMB, memErr := system.GetMemoryMB()
 	if memErr != nil {
 		m.logger.Printf("[WARN] Cannot read system memory: %v — skipping memory check", memErr)
 	} else {
 		usableMB := totalMB - reservedMB
-		currentReqMB, currentLimitMB := m.CommittedMemory()
 		newReqMB := ParseMemoryMB(meta.Resources.MemRequest)
-		newLimitMB := ParseMemoryMB(meta.Resources.MemLimit)
 
-		m.logger.Printf("[INFO] Memory check: total=%dMB, reserved=%dMB, usable=%dMB, committed_req=%dMB, new_req=%dMB, remaining=%dMB",
-			totalMB, reservedMB, usableMB, currentReqMB, newReqMB, usableMB-currentReqMB-newReqMB)
+		m.logger.Printf("[INFO] Memory check: total=%dMB, reserved=%dMB, usable=%dMB, real_used=%dMB, new_req=%dMB, remaining=%dMB",
+			totalMB, reservedMB, usableMB, usedMB, newReqMB, usableMB-usedMB-newReqMB)
 
-		// Hard block: requests exceed usable memory
-		if newReqMB > 0 && currentReqMB+newReqMB > usableMB {
+		// Hard block: real used + new request exceeds usable memory
+		if newReqMB > 0 && usedMB+newReqMB > usableMB {
 			return "", fmt.Errorf(
 				"Nincs elég memória az alkalmazás telepítéséhez. "+
 					"Szükséges: %d MB, Elérhető: %d MB "+
-					"(összesen: %d MB, ebből %d MB már foglalt, %d MB rendszer számára fenntartva)",
+					"(összesen: %d MB, ebből %d MB használt, %d MB rendszer számára fenntartva)",
 				newReqMB,
-				usableMB-currentReqMB,
+				usableMB-usedMB,
 				totalMB,
-				currentReqMB,
+				usedMB,
 				reservedMB,
 			)
 		}
 
 		// Soft warning: limits exceed total (overcommit)
+		_, currentLimitMB := m.CommittedMemory()
+		newLimitMB := ParseMemoryMB(meta.Resources.MemLimit)
 		if newLimitMB > 0 && currentLimitMB+newLimitMB > totalMB {
 			deployWarning = "Az alkalmazások csúcsterhelése meghaladhatja a rendelkezésre álló memóriát. " +
 				"Normál használat mellett ez nem okoz problémát."