Add cascading fallback for deal titles instead of hardcoded "Unknown"

Replace the simple nil-title → "Unknown" logic in printDeal with a
fallbackDealTitle() function that tries multiple fields in priority
order before giving up:

  1. Title (cleaned) — the happy path, same as before
  2. Brand + Department — e.g. "Publix deal (Meat)"
  3. Brand alone — e.g. "Publix deal"
  4. Department alone — e.g. "Meat deal"
  5. Description truncated to 48 chars — last-resort meaningful text
  6. Item ID — e.g. "Deal 12345"
  7. "Untitled deal" — only when every field is empty

This makes the output more useful for the ~5-10% of weekly ad items
that ship with a nil Title from the Publix API, which previously all
showed as "Unknown" and were indistinguishable from each other.

Tests:
- TestPrintDeals_FallbackTitleFromBrandAndDepartment
- TestPrintDeals_FallbackTitleFromID

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

internal/display/formatter_test.go

@@ -55,6 +55,41 @@ func TestPrintDeals_ContainsExpectedContent(t *testing.T) {
 	assert.NotContains(t, output, "&")
 }
 
+func TestPrintDeals_FallbackTitleFromBrandAndDepartment(t *testing.T) {
+	items := []api.SavingItem{
+		{
+			ID:         "fallback-1",
+			Title:      nil,
+			Brand:      ptr("Publix"),
+			Department: ptr("Meat"),
+			Categories: []string{"meat"},
+		},
+	}
+
+	var buf bytes.Buffer
+	display.PrintDeals(&buf, items)
+	output := buf.String()
+
+	assert.Contains(t, output, "Publix deal (Meat)")
+	assert.NotContains(t, output, "Unknown")
+}
+
+func TestPrintDeals_FallbackTitleFromID(t *testing.T) {
+	items := []api.SavingItem{
+		{
+			ID:    "fallback-2",
+			Title: nil,
+		},
+	}
+
+	var buf bytes.Buffer
+	display.PrintDeals(&buf, items)
+	output := buf.String()
+
+	assert.Contains(t, output, "Deal fallback-2")
+	assert.NotContains(t, output, "Unknown")
+}
+
 func TestPrintDealsJSON(t *testing.T) {
 	var buf bytes.Buffer
 	err := display.PrintDealsJSON(&buf, sampleDeals())