Refactor: reduce code duplication with shared abstractions

- Add BaseClient HTTP abstraction (internal/api/http.go) to eliminate
  duplicated HTTP boilerplate across Todoist, Trello, and PlanToEat clients
- Add response helpers (internal/handlers/response.go) for JSON/HTML responses
- Add generic cache wrapper (internal/handlers/cache.go) using Go generics
- Consolidate HandleCompleteAtom/HandleUncompleteAtom into handleAtomToggle
- Merge TabsHandler into Handler, delete tabs.go
- Extract sortTasksByUrgency and filterAndSortTrelloTasks helpers
- Update tests to work with new BaseClient structure

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

1 files changed, 13 insertions, 25 deletions

diff --git a/internal/api/todoist_test.go b/internal/api/todoist_test.go
index 56b1484..88f94f8 100644
--- a/internal/api/todoist_test.go
+++ b/internal/api/todoist_test.go
@@ -10,6 +10,14 @@ import (
 	"time"
 )
 
+// newTestTodoistClient creates a TodoistClient for testing with custom base URL
+func newTestTodoistClient(baseURL, apiKey string) *TodoistClient {
+	client := NewTodoistClient(apiKey)
+	client.BaseClient.BaseURL = baseURL
+	client.syncClient.BaseURL = baseURL
+	return client
+}
+
 func TestTodoistClient_CreateTask(t *testing.T) {
 	// Mock server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -59,11 +67,7 @@ func TestTodoistClient_CreateTask(t *testing.T) {
 	defer server.Close()
 
 	// Create client with mock server URL
-	client := &TodoistClient{
-		apiKey:     "test-key",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTodoistClient(server.URL, "test-key")
 
 	// Test CreateTask
 	ctx := context.Background()
@@ -122,11 +126,7 @@ func TestTodoistClient_CreateTask_WithDueDate(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TodoistClient{
-		apiKey:     "test-key",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTodoistClient(server.URL, "test-key")
 
 	// Test CreateTask with due date
 	ctx := context.Background()
@@ -170,11 +170,7 @@ func TestTodoistClient_CompleteTask(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TodoistClient{
-		apiKey:     "test-key",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTodoistClient(server.URL, "test-key")
 
 	// Test CompleteTask
 	ctx := context.Background()
@@ -194,11 +190,7 @@ func TestTodoistClient_CompleteTask_Error(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TodoistClient{
-		apiKey:     "test-key",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTodoistClient(server.URL, "test-key")
 
 	// Test CompleteTask with error
 	ctx := context.Background()
@@ -235,11 +227,7 @@ func TestTodoistClient_GetProjects(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TodoistClient{
-		apiKey:     "test-key",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTodoistClient(server.URL, "test-key")
 
 	// Test GetProjects
 	ctx := context.Background()