feat: add title support and summary cleanup to pushover provider

[Skrotdev]

📑 Description

This PR improves Pushover notifications for incident workflows.
It adds support for sending an incident title and improves message formatting so notifications are cleaner and easier to read.

• Added optional title support for Pushover notifications.
• Cleaned message text by removing paragraph HTML tags (<p> and </p>).
• Kept existing runtime options (sound, priority, retry, expire) working as before.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

Fixes #6105

• Follow-up to feat: add sound and priority support to pushover provider #5211 (sound/priority support): this PR adds title support and message paragraph cleanup, without changing existing sound/priority behavior.

[greptile-apps]

Target branch is not in the allowed branches list.

[vercel]

@Skrotdev is attempting to deploy a commit to the KeepHQ Team on Vercel.

A member of the Team first needs to authorize it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.49%. Comparing base (5fc042d) to head (eab713d).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5710       +/-   ##
===========================================
- Coverage   46.41%   30.49%   -15.92%     
===========================================
  Files         176      101       -75     
  Lines       18443    11689     -6754     
===========================================
- Hits         8561     3565     -4996     
+ Misses       9882     8124     -1758     

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[shahargl]

lgtm

[github-actions]

🌟 Well done @Skrotdev! Two PRs merged already! 🎉🥳

With your second PR, you're on a roll, and your contributions are already making a difference. 🌟
Looking forward to seeing even more contributions from you. See you in Slack https://slack.keephq.dev 🚀