[feat] add ntfy as a new alert notification channel

[Zmjjeff7]

What is changed and how it works?

This PR adds ntfy as a new alert notification channel
(type=15) to HertzBeat. ntfy is a popular open-source HTTP-based
push-notification service that is widely used in self-hosting communities,
and it works well for receiving HertzBeat alerts on mobile devices and
desktops without depending on third-party platforms.

Backend changes

• New handler NtfyAlertNotifyHandlerImpl in hertzbeat-alerter,
  extending AbstractAlertNotifyHandlerImpl with type id 15
• Three new fields on NoticeReceiver: ntfyServerUrl, ntfyTopic,
  ntfyToken
• New configurable property alerter.ntfy-default-server-url
  (default: https://ntfy.sh)

Feature highlights

• Priority mapping — alert severity is mapped to ntfy priority levels
  (critical=5, warning=4, info/unknown=3, resolved alerts=2)
• Emoji tags — status- and severity-aware tags
  (rotating_light + skull for critical firing, warning for warning,
  white_check_mark for resolved); the alertname is also appended as a
  plain-text tag
• Bearer token auth — supports self-hosted ntfy instances with
  access-control tokens
• Click action — notifications carry a click URL pointing to the
  HertzBeat console
• Markdown body — alert content is rendered in Markdown for
  better readability on ntfy clients

Frontend changes

• Added ntfy option to the notification receiver type dropdown
• Three new form fields: server URL (optional, default
  https://ntfy.sh), topic (required), access token (optional)
• Display tag in the receiver list table
• i18n translations for en-US, zh-CN, zh-TW, ja-JP, pt-BR

Tests

Added NtfyAlertNotifyHandlerImplTest with 16 test cases covering:

• Successful send / non-2xx response / network errors
• URL building (custom server, default server fallback,
  trailing-slash handling)
• Bearer token header injection
• Priority mapping for all severity levels and resolved state
• Tag generation for critical/warning/info/resolved cases
• Header presence and values (Priority, Tags, Click, Markdown)

Checklist

• I have read the Contribution Guidelines
• I have self-reviewed my code
• I have added unit tests covering the new feature
• My change follows the existing alert handler conventions
  (Gotify/ServerChan style)
• No HIP is required (new notification channel — small enhancement)

[tomsun28]

hi please help fix the ci error. thanks

[tomsun28]

hi the ci show that web-app still has the eslint error, you can run pnpm run lint:fix to fix this. https://github.com/apache/hertzbeat/actions/runs/26349762920/job/77565809007#step:6:24