Fix datetime filter: use genuine UTC for presets, consistent time format

- Use toISOString() instead of format() with literal 'Z' suffix to
  produce correct UTC timestamps for preset intervals
- Default time to '00:00:00' (with seconds) for format consistency
- Remove redundant output() override inherited from base class

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gugu

frontend/src/app/components/ui-components/filter-fields/date-time/date-time.component.spec.ts

@@ -124,7 +124,7 @@ describe('DateTimeFilterComponent', () => {
 		const fieldEvent = vi.spyOn(component.onFieldChange, 'emit');
 		component.onDateChange();
 
-		expect(component.time).toEqual('00:00');
-		expect(fieldEvent).toHaveBeenCalledWith('2021-08-26T00:00Z');
+		expect(component.time).toEqual('00:00:00');
+		expect(fieldEvent).toHaveBeenCalledWith('2021-08-26T00:00:00Z');
 	});
 });

frontend/src/app/components/ui-components/filter-fields/date-time/date-time.component.ts

@@ -1,5 +1,5 @@
 import { CommonModule } from '@angular/common';
-import { AfterViewInit, Component, ElementRef, Input, OnInit, output, ViewChild } from '@angular/core';
+import { AfterViewInit, Component, ElementRef, Input, OnInit, ViewChild } from '@angular/core';
 import { FormsModule } from '@angular/forms';
 import { MatFormFieldModule } from '@angular/material/form-field';
 import { MatInputModule } from '@angular/material/input';
@@ -17,8 +17,6 @@ export class DateTimeFilterComponent extends BaseFilterFieldComponent implements
 	@Input() value: string;
 	@ViewChild('inputElement') inputElement: ElementRef<HTMLInputElement>;
 
-	override readonly onFieldChange = output<any>();
-
 	public filterMode: string = 'last_day';
 	public date: string;
 	public time: string;
@@ -68,7 +66,7 @@ export class DateTimeFilterComponent extends BaseFilterFieldComponent implements
 	}
 
 	onDateChange(): void {
-		if (!this.time) this.time = '00:00';
+		if (!this.time) this.time = '00:00:00';
 		const datetime = `${this.date}T${this.time}Z`;
 		this.onFieldChange.emit(datetime);
 		this.onComparatorChange.emit(this.filterMode);
@@ -108,6 +106,6 @@ export class DateTimeFilterComponent extends BaseFilterFieldComponent implements
 				targetDate = now;
 		}
 
-		return format(targetDate, "yyyy-MM-dd'T'HH:mm:ss'Z'");
+		return targetDate.toISOString().replace(/\.\d{3}Z$/, 'Z');
 	}
 }