feat(api): Add get_headline_at_cursor to Agenda api

Closes #816

Author: kristijanhusak

lua/orgmode/api/agenda.lua

@@ -102,4 +102,22 @@ function OrgAgenda.open_by_key(key)
   return orgmode.agenda:open_by_key(key)
 end
 
+---Get the headline at the cursor position in the agenda view
+---@return OrgApiHeadline | nil
+function OrgAgenda.get_headline_at_cursor()
+  local line_nr = vim.fn.line('.')
+  local agenda_views = orgmode.agenda.views
+
+  for _, view in ipairs(agenda_views) do
+    local agenda_line = view:get_line(line_nr)
+    if agenda_line then
+      local headline = agenda_line.headline
+      if headline then
+        local file = require('orgmode.api').load(headline.file.filename)
+        return file:get_headline_on_line(headline:get_range().start_line)
+      end
+    end
+  end
+end
+
 return OrgAgenda

lua/orgmode/api/file.lua

@@ -93,6 +93,14 @@ function OrgFile:get_closest_headline(cursor)
   return nil
 end
 
+---@param line_number number
+---@return OrgApiHeadline | nil
+function OrgFile:get_headline_on_line(line_number)
+  return vim.tbl_filter(function(headline)
+    return headline.position.start_line == line_number
+  end, self.headlines)[1]
+end
+
 --- Get a link destination as string
 ---
 --- Depending if org_id_link_to_org_use_id is set the format is