feat(agenda): highlight upcoming deadlines as @org.agenda.deadline.upcoming

[vollowx]

AI-assisted: Claude Sonnet 4.6 from GitHub Copilot

Summary

Added @org.agenda.deadline.upcoming for upcoming deadlines, especially for the deadline items shown at today.

Before:

After: Upcoming deadline items shown at today are no longer highlighted as scheduled_past.

Related Issues

Closes #1137

Changes

• Added a new highlight @org.agenda.deadline.upcoming defaults to the same style as @org.agenda.scheduled_past
  • lua/orgmode/colors/highlights.lua
  • lua/orgmode/colors/init.lua
• Highlight upcoming deadlines shown e.g. at today as the highlight above, in lua/orgmode/agenda/agenda_item.lua
• Update tests in agenda/agenda_item_spec.lua and color/color_specs.lua to use the new highlight name

Notes:

I updated the tests yet when I do make test, there're some not passing but unrelated to this MR.

Also I'd suggest to change ...scheduled_past to ...scheduled.past, and make it clearer in the code, that is to stop using warning and use the highlight names directly.

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.

[kristijanhusak]

Looks good, thanks!

[vollowx]

Thanks for your quick response!

As mentioned above, I'd suggest to:

1. Rename @org.agenda.scheduled_past --> @org.agenda.scheduled.past to follow the treesitter highlight convention
2. Stop using warning to refer to scheduled_past hl in code, instead use directly scheduled_past.

I'd like to know your opinions on this!