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, 11 insertions, 24 deletions

diff --git a/internal/api/trello_test.go b/internal/api/trello_test.go
index b43b55e..7433ff0 100644
--- a/internal/api/trello_test.go
+++ b/internal/api/trello_test.go
@@ -12,6 +12,13 @@ import (
 	"time"
 )
 
+// newTestTrelloClient creates a TrelloClient for testing with custom base URL
+func newTestTrelloClient(baseURL, apiKey, token string) *TrelloClient {
+	client := NewTrelloClient(apiKey, token)
+	client.BaseClient.BaseURL = baseURL
+	return client
+}
+
 func TestTrelloClient_CreateCard(t *testing.T) {
 	// Mock server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -65,12 +72,7 @@ func TestTrelloClient_CreateCard(t *testing.T) {
 	defer server.Close()
 
 	// Create client with mock server URL
-	client := &TrelloClient{
-		apiKey:     "test-key",
-		token:      "test-token",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTrelloClient(server.URL, "test-key", "test-token")
 
 	// Test CreateCard
 	ctx := context.Background()
@@ -125,12 +127,7 @@ func TestTrelloClient_CreateCard_WithDueDate(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TrelloClient{
-		apiKey:     "test-key",
-		token:      "test-token",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTrelloClient(server.URL, "test-key", "test-token")
 
 	// Test CreateCard with due date
 	ctx := context.Background()
@@ -184,12 +181,7 @@ func TestTrelloClient_UpdateCard(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TrelloClient{
-		apiKey:     "test-key",
-		token:      "test-token",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTrelloClient(server.URL, "test-key", "test-token")
 
 	// Test UpdateCard
 	ctx := context.Background()
@@ -214,12 +206,7 @@ func TestTrelloClient_UpdateCard_Error(t *testing.T) {
 	defer server.Close()
 
 	// Create client
-	client := &TrelloClient{
-		apiKey:     "test-key",
-		token:      "test-token",
-		baseURL:    server.URL,
-		httpClient: &http.Client{},
-	}
+	client := newTestTrelloClient(server.URL, "test-key", "test-token")
 
 	// Test UpdateCard with error
 	ctx := context.Background()