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, 36 insertions, 0 deletions

diff --git a/internal/handlers/response.go b/internal/handlers/response.go
new file mode 100644
index 0000000..3976f02
--- /dev/null
+++ b/internal/handlers/response.go
@@ -0,0 +1,36 @@
+package handlers
+
+import (
+	"encoding/json"
+	"html/template"
+	"log"
+	"net/http"
+)
+
+// 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)
+}
+
+// JSONError writes an error response as JSON
+func JSONError(w http.ResponseWriter, status int, msg string, err error) {
+	if err != nil {
+		log.Printf("Error: %s: %v", msg, err)
+	}
+	http.Error(w, msg, status)
+}
+
+// HTMLResponse renders an HTML template
+func HTMLResponse(w http.ResponseWriter, tmpl *template.Template, name string, data interface{}) {
+	if err := tmpl.ExecuteTemplate(w, name, data); err != nil {
+		http.Error(w, "Failed to render template", http.StatusInternalServerError)
+		log.Printf("Error rendering template %s: %v", name, err)
+	}
+}
+
+// HTMLString writes an HTML string directly
+func HTMLString(w http.ResponseWriter, html string) {
+	w.Header().Set("Content-Type", "text/html")
+	w.Write([]byte(html))
+}