fix: update tests for briefing rewrite and raised content cap

- Remove test_slot_greeting — slot_greeting() was removed in the
  conversational briefing rewrite
- Update test_extract_item_truncates_content to use CONTENT_MAX_CHARS
  rather than a hardcoded 2000 (cap raised to 50000 for full articles)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_briefing_pipeline.py

@@ -21,13 +21,6 @@ def test_format_task_for_briefing():
     assert "in_progress" in result or "In Progress" in result
 
 
-def test_slot_greeting():
-    """slot_greeting() should return different strings for different slot names."""
-    from fabledassistant.services.briefing_pipeline import slot_greeting
-    assert "morning" in slot_greeting("compilation").lower() or slot_greeting("compilation")
-    assert slot_greeting("morning") != slot_greeting("midday")
-    assert slot_greeting("midday") != slot_greeting("afternoon")
-
 
 def test_compute_task_snapshot_hash():
     """compute_task_hash should return a stable SHA-256 hex string."""