feat: Implement announcements

[TwiN]

Summary

Fixes #1203

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Updated documentation in README.md, if applicable.

[Copilot]

Pull Request Overview

This PR implements a comprehensive announcements system that allows displaying important system-wide messages at the top of the status page. The feature includes announcement configuration, timeline-based display with visual type indicators, and automatic refresh functionality.

• Adds announcement configuration support with validation and type-specific styling
• Creates a collapsible timeline UI component with dark mode support
• Integrates announcements into the API endpoint and frontend data flow

Reviewed Changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
web/static/css/app.css	Updates compiled CSS with new announcement styling classes and animations
web/app/src/views/Home.vue	Integrates AnnouncementBanner component and passes announcements prop
web/app/src/components/AnnouncementBanner.vue	New Vue component with timeline UI for displaying announcements
web/app/src/App.vue	Adds announcement fetching and periodic refresh logic
config/config.go	Adds announcements field to Config struct with validation
config/announcement/announcement.go	New package defining announcement types and validation logic
api/config_test.go	Updates test to match new JSON response format including announcements
api/config.go	Modifies config endpoint to include announcements in response
api/api.go	Updates ConfigHandler initialization to include config reference
README.md	Documents announcements configuration and usage

Comments suppressed due to low confidence (1)

api/config.go:34

• [nitpick] Using []interface{}{} is inconsistent with the typed approach used when announcements exist. Consider using a consistent type like []*announcement.Announcement{} or define a proper response struct.

		response["announcements"] = []interface{}{}

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