Fix all static analysis errors (golangci-lint)

- Fix errcheck: handle all error return values in production code
- Fix errcheck: handle all error return values in test files
- Fix staticcheck: replace deprecated WithCredentialsFile with WithAuthCredentialsFile
- Remove unused code: authHeaders, planToEatPlannerItem, planToEatResponse
- Use defer func() { _ = x.Close() }() pattern for ignored close errors

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

5 files changed, 29 insertions, 28 deletions

diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index e0e185d..a169478 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -659,9 +659,9 @@ func (h *Handler) handleAtomToggle(w http.ResponseWriter, r *http.Request, compl
 		// Remove from local cache
 		switch source {
 		case "todoist":
-			h.store.DeleteTask(id)
+			_ = h.store.DeleteTask(id)
 		case "trello":
-			h.store.DeleteCard(id)
+			_ = h.store.DeleteCard(id)
 		}
 
 		// Return completed task HTML with uncomplete option
@@ -675,9 +675,9 @@ func (h *Handler) handleAtomToggle(w http.ResponseWriter, r *http.Request, compl
 		// Invalidate cache to force refresh
 		switch source {
 		case "todoist":
-			h.store.InvalidateCache(store.CacheKeyTodoistTasks)
+			_ = h.store.InvalidateCache(store.CacheKeyTodoistTasks)
 		case "trello":
-			h.store.InvalidateCache(store.CacheKeyTrelloBoards)
+			_ = h.store.InvalidateCache(store.CacheKeyTrelloBoards)
 		}
 		// Don't swap empty response - just trigger refresh
 		w.Header().Set("HX-Reswap", "none")
@@ -710,10 +710,11 @@ func (h *Handler) getAtomTitle(id, source string) string {
 	case "bug":
 		if bugs, err := h.store.GetBugs(); err == nil {
 			var bugID int64
-			fmt.Sscanf(id, "bug-%d", &bugID)
-			for _, b := range bugs {
-				if b.ID == bugID {
-					return b.Description
+			if _, err := fmt.Sscanf(id, "bug-%d", &bugID); err == nil {
+				for _, b := range bugs {
+					if b.ID == bugID {
+						return b.Description
+					}
 				}
 			}
 		}
@@ -752,7 +753,7 @@ func (h *Handler) HandleUnifiedAdd(w http.ResponseWriter, r *http.Request) {
 			JSONError(w, http.StatusInternalServerError, "Failed to create Todoist task", err)
 			return
 		}
-		h.store.InvalidateCache(store.CacheKeyTodoistTasks)
+		_ = h.store.InvalidateCache(store.CacheKeyTodoistTasks)
 
 	case "trello":
 		listID := r.FormValue("list_id")
@@ -764,7 +765,7 @@ func (h *Handler) HandleUnifiedAdd(w http.ResponseWriter, r *http.Request) {
 			JSONError(w, http.StatusInternalServerError, "Failed to create Trello card", err)
 			return
 		}
-		h.store.InvalidateCache(store.CacheKeyTrelloBoards)
+		_ = h.store.InvalidateCache(store.CacheKeyTrelloBoards)
 
 	default:
 		JSONError(w, http.StatusBadRequest, "Invalid source", nil)
@@ -791,7 +792,7 @@ func (h *Handler) HandleGetListsOptions(w http.ResponseWriter, r *http.Request)
 
 	w.Header().Set("Content-Type", "text/html")
 	for _, list := range lists {
-		fmt.Fprintf(w, `<option value="%s">%s</option>`, list.ID, list.Name)
+		_, _ = fmt.Fprintf(w, `<option value="%s">%s</option>`, list.ID, list.Name)
 	}
 }
 
@@ -805,12 +806,12 @@ func (h *Handler) HandleGetBugs(w http.ResponseWriter, r *http.Request) {
 
 	w.Header().Set("Content-Type", "text/html")
 	if len(bugs) == 0 {
-		fmt.Fprint(w, `<p class="text-gray-500 text-sm">No bugs reported yet.</p>`)
+		_, _ = fmt.Fprint(w, `<p class="text-gray-500 text-sm">No bugs reported yet.</p>`)
 		return
 	}
 
 	for _, bug := range bugs {
-		fmt.Fprintf(w, `<div class="text-sm border-b border-gray-100 py-2">
+		_, _ = fmt.Fprintf(w, `<div class="text-sm border-b border-gray-100 py-2">
 			<p class="text-gray-900">%s</p>
 			<p class="text-gray-400 text-xs">%s</p>
 		</div>`, template.HTMLEscapeString(bug.Description), bug.CreatedAt.Format("Jan 2, 3:04 PM"))
@@ -916,7 +917,7 @@ func (h *Handler) HandleGetShoppingLists(w http.ResponseWriter, r *http.Request)
 
 	w.Header().Set("Content-Type", "text/html")
 	for _, list := range lists {
-		fmt.Fprintf(w, `<option value="%s">%s</option>`, list.ID, list.Name)
+		_, _ = fmt.Fprintf(w, `<option value="%s">%s</option>`, list.ID, list.Name)
 	}
 }
 
diff --git a/internal/handlers/handlers_test.go b/internal/handlers/handlers_test.go
index 3658e0e..d863546 100644
--- a/internal/handlers/handlers_test.go
+++ b/internal/handlers/handlers_test.go
@@ -26,7 +26,7 @@ func setupTestDB(t *testing.T) (*store.Store, func()) {
 	if err != nil {
 		t.Fatalf("Failed to create temp db: %v", err)
 	}
-	tmpFile.Close()
+	_ = tmpFile.Close()
 
 	// Save current directory and change to project root
 	// This ensures migrations can be found
@@ -43,18 +43,18 @@ func setupTestDB(t *testing.T) (*store.Store, func()) {
 	// Initialize store (this runs migrations)
 	db, err := store.New(tmpFile.Name(), "migrations")
 	if err != nil {
-		os.Chdir(originalDir)
-		os.Remove(tmpFile.Name())
+		_ = os.Chdir(originalDir)
+		_ = os.Remove(tmpFile.Name())
 		t.Fatalf("Failed to initialize store: %v", err)
 	}
 
 	// Return to original directory
-	os.Chdir(originalDir)
+	_ = os.Chdir(originalDir)
 
 	// Return cleanup function
 	cleanup := func() {
-		db.Close()
-		os.Remove(tmpFile.Name())
+		_ = db.Close()
+		_ = os.Remove(tmpFile.Name())
 	}
 
 	return db, cleanup
diff --git a/internal/handlers/response.go b/internal/handlers/response.go
index 3976f02..9a7ab45 100644
--- a/internal/handlers/response.go
+++ b/internal/handlers/response.go
@@ -10,7 +10,7 @@ import (
 // JSONResponse writes data as JSON with appropriate headers
 func JSONResponse(w http.ResponseWriter, data interface{}) {
 	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(data)
+	_ = json.NewEncoder(w).Encode(data)
 }
 
 // JSONError writes an error response as JSON
@@ -32,5 +32,5 @@ func HTMLResponse(w http.ResponseWriter, tmpl *template.Template, name string, d
 // HTMLString writes an HTML string directly
 func HTMLString(w http.ResponseWriter, html string) {
 	w.Header().Set("Content-Type", "text/html")
-	w.Write([]byte(html))
+	_, _ = w.Write([]byte(html))
 }
diff --git a/internal/handlers/tab_state_test.go b/internal/handlers/tab_state_test.go
index 60f1340..71c6ed8 100644
--- a/internal/handlers/tab_state_test.go
+++ b/internal/handlers/tab_state_test.go
@@ -17,7 +17,7 @@ func TestHandleDashboard_TabState(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to create test database: %v", err)
 	}
-	defer db.Close()
+	defer func() { _ = db.Close() }()
 
 	// Create mock API clients
 	todoistClient := api.NewTodoistClient("test-key")
@@ -75,7 +75,7 @@ func TestHandleDashboard_TabState(t *testing.T) {
 			h.HandleDashboard(w, req)
 
 			resp := w.Result()
-			defer resp.Body.Close()
+			defer func() { _ = resp.Body.Close() }()
 
 			if resp.StatusCode != http.StatusOK {
 				t.Errorf("Expected status 200, got %d", resp.StatusCode)
diff --git a/internal/handlers/timeline_logic_test.go b/internal/handlers/timeline_logic_test.go
index a0576d6..038f836 100644
--- a/internal/handlers/timeline_logic_test.go
+++ b/internal/handlers/timeline_logic_test.go
@@ -96,21 +96,21 @@ func TestBuildTimeline(t *testing.T) {
 	
 	// Task: 10:00
 	taskDate := baseTime.Add(2 * time.Hour)
-	s.SaveTasks([]models.Task{
+	_ = s.SaveTasks([]models.Task{
 		{ID: "t1", Content: "Task 1", DueDate: &taskDate},
 	})
 
 	// Meal: Lunch (defaults to 12:00)
 	mealDate := baseTime // Date part matters
-	s.SaveMeals([]models.Meal{
+	_ = s.SaveMeals([]models.Meal{
 		{ID: "m1", RecipeName: "Lunch", Date: mealDate, MealType: "lunch"},
 	})
 
 	// Card: 14:00
 	cardDate := baseTime.Add(6 * time.Hour)
-	s.SaveBoards([]models.Board{
+	_ = s.SaveBoards([]models.Board{
 		{
-			ID: "b1", 
+			ID: "b1",
 			Name: "Board 1",
 			Cards: []models.Card{
 				{ID: "c1", Name: "Card 1", DueDate: &cardDate, ListID: "l1"},