fix: address review findings for observability PR

1. Security: Replace insecure extractRemoteIP() in audit service with
   middleware.RealIP() which validates trusted proxies before trusting
   X-Real-IP/X-Forwarded-For headers. Export RealIP from middleware.
   Update audit tests to verify anti-spoofing behavior.

2. Audit coverage: Add audit instrumentation to all 9 handlers that
   had dead action constants: HandleEnvVarSave, HandleLabelAdd,
   HandleLabelEdit, HandleLabelDelete, HandleVolumeAdd, HandleVolumeEdit,
   HandleVolumeDelete, HandlePortAdd, HandlePortDelete.

3. README: Fix API path from /api/audit to /api/v1/audit.

4. README: Fix duplicate numbering in DI order section (items 10-11
   were listed twice, now correctly numbered 10-16).

internal/handlers/app.go

@@ -1023,6 +1023,10 @@ func (h *Handlers) HandleEnvVarSave() http.HandlerFunc {
 			return
 		}
 
+		h.auditLog(request, models.AuditActionEnvVarSave,
+			models.AuditResourceEnvVar, application.ID,
+			fmt.Sprintf("saved %d env vars", len(modelPairs)))
+
 		h.respondJSON(writer, request, map[string]bool{"ok": true}, http.StatusOK)
 	}
 }
@@ -1039,7 +1043,13 @@ func (h *Handlers) HandleLabelAdd() http.HandlerFunc {
 				label.Key = key
 				label.Value = value
 
-				return label.Save(ctx)
+				err := label.Save(ctx)
+				if err == nil {
+					h.auditLog(request, models.AuditActionLabelAdd,
+						models.AuditResourceLabel, application.ID, "added label: "+key)
+				}
+
+				return err
 			},
 		)
 	}
@@ -1068,6 +1078,9 @@ func (h *Handlers) HandleLabelDelete() http.HandlerFunc {
 		deleteErr := label.Delete(request.Context())
 		if deleteErr != nil {
 			h.log.Error("failed to delete label", "error", deleteErr)
+		} else {
+			h.auditLog(request, models.AuditActionLabelDelete,
+				models.AuditResourceLabel, appID, "deleted label: "+label.Key)
 		}
 
 		http.Redirect(writer, request, "/apps/"+appID, http.StatusSeeOther)
@@ -1125,6 +1138,10 @@ func (h *Handlers) HandleVolumeAdd() http.HandlerFunc {
 		saveErr := volume.Save(request.Context())
 		if saveErr != nil {
 			h.log.Error("failed to add volume", "error", saveErr)
+		} else {
+			h.auditLog(request, models.AuditActionVolumeAdd,
+				models.AuditResourceVolume, application.ID,
+				"added volume: "+hostPath+":"+containerPath)
 		}
 
 		http.Redirect(writer, request, "/apps/"+application.ID, http.StatusSeeOther)
@@ -1154,6 +1171,10 @@ func (h *Handlers) HandleVolumeDelete() http.HandlerFunc {
 		deleteErr := volume.Delete(request.Context())
 		if deleteErr != nil {
 			h.log.Error("failed to delete volume", "error", deleteErr)
+		} else {
+			h.auditLog(request, models.AuditActionVolumeDelete,
+				models.AuditResourceVolume, appID,
+				"deleted volume: "+volume.HostPath+":"+volume.ContainerPath)
 		}
 
 		http.Redirect(writer, request, "/apps/"+appID, http.StatusSeeOther)
@@ -1203,6 +1224,10 @@ func (h *Handlers) HandlePortAdd() http.HandlerFunc {
 		saveErr := port.Save(request.Context())
 		if saveErr != nil {
 			h.log.Error("failed to save port", "error", saveErr)
+		} else {
+			h.auditLog(request, models.AuditActionPortAdd,
+				models.AuditResourcePort, application.ID,
+				fmt.Sprintf("added port: %d:%d/%s", hostPort, containerPort, protocol))
 		}
 
 		http.Redirect(writer, request, "/apps/"+application.ID, http.StatusSeeOther)
@@ -1249,6 +1274,10 @@ func (h *Handlers) HandlePortDelete() http.HandlerFunc {
 		deleteErr := port.Delete(request.Context())
 		if deleteErr != nil {
 			h.log.Error("failed to delete port", "error", deleteErr)
+		} else {
+			h.auditLog(request, models.AuditActionPortDelete,
+				models.AuditResourcePort, appID,
+				fmt.Sprintf("deleted port: %d:%d/%s", port.HostPort, port.ContainerPort, port.Protocol))
 		}
 
 		http.Redirect(writer, request, "/apps/"+appID, http.StatusSeeOther)
@@ -1324,6 +1353,9 @@ func (h *Handlers) HandleLabelEdit() http.HandlerFunc {
 		saveErr := label.Save(request.Context())
 		if saveErr != nil {
 			h.log.Error("failed to update label", "error", saveErr)
+		} else {
+			h.auditLog(request, models.AuditActionLabelEdit,
+				models.AuditResourceLabel, appID, "edited label: "+key)
 		}
 
 		http.Redirect(writer, request, "/apps/"+appID, http.StatusSeeOther)
@@ -1382,6 +1414,10 @@ func (h *Handlers) HandleVolumeEdit() http.HandlerFunc {
 		saveErr := volume.Save(request.Context())
 		if saveErr != nil {
 			h.log.Error("failed to update volume", "error", saveErr)
+		} else {
+			h.auditLog(request, models.AuditActionVolumeEdit,
+				models.AuditResourceVolume, appID,
+				"edited volume: "+hostPath+":"+containerPath)
 		}
 
 		http.Redirect(writer, request, "/apps/"+appID, http.StatusSeeOther)