fix: cursor row text invisible on completed tasks

[aquinoonell]

Closes #116

Fix
Two changes in task_row.rs:

• Glyph color : when the row is the cursor row, use
  theme.accent instead of theme.done for the glyph so it
  stays visible on the cursor background.
• Body text base color : when the row is the cursor row,
  use theme.fg instead of theme.done so the task body text is
  visible.

Testing
Tested by navigating to a completed task in the archive view.
After the fix, the task text and glyph are visible on the cursor row
across default themes.

@mikenikles