feat(conflict): show branch names in virtual text labels

Problem: virtual text showed generic "current"/"incoming" labels with
no indication of which branch each side came from.

Solution: extract the branch name from the marker line itself
(e.g. <<<<<<< HEAD, >>>>>>> feature) and display as
"HEAD (current)" / "feature (incoming)".

lua/diffs/conflict.lua

@@ -107,8 +107,15 @@ local function apply_highlights(bufnr, regions, config)
     })
 
     if config.show_virtual_text then
+      local ours_line = vim.api.nvim_buf_get_lines(
+        bufnr,
+        region.marker_ours,
+        region.marker_ours + 1,
+        false
+      )[1] or ''
+      local ours_name = ours_line:match('^<<<<<<<%s+(.+)$') or ''
       pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_ours, 0, {
-        virt_text = { { ' current', 'DiffsConflictMarker' } },
+        virt_text = { { ' ' .. ours_name .. ' (current)', 'DiffsConflictMarker' } },
         virt_text_pos = 'eol',
       })
     end
@@ -176,8 +183,15 @@ local function apply_highlights(bufnr, regions, config)
     })
 
     if config.show_virtual_text then
+      local theirs_line = vim.api.nvim_buf_get_lines(
+        bufnr,
+        region.marker_theirs,
+        region.marker_theirs + 1,
+        false
+      )[1] or ''
+      local theirs_name = theirs_line:match('^>>>>>>>%s+(.+)$') or ''
       pcall(vim.api.nvim_buf_set_extmark, bufnr, ns, region.marker_theirs, 0, {
-        virt_text = { { ' incoming', 'DiffsConflictMarker' } },
+        virt_text = { { ' ' .. theirs_name .. ' (incoming)', 'DiffsConflictMarker' } },
         virt_text_pos = 'eol',
       })
     end