Add initial backend implementation

- Go module with Gin, GORM, JWT, excelize dependencies
- Configuration loading from YAML with all settings
- GORM models for users, categories, components, configurations, alerts
- Repository layer for all entities
- Services: auth (JWT), pricing (median/average/weighted), components,
  quotes, configurations, export (CSV/XLSX), alerts
- Middleware: JWT auth, role-based access, CORS
- HTTP handlers for all API endpoints
- Main server with dependency injection and graceful shutdown

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

internal/handlers/component.go

@@ -0,0 +1,72 @@
+package handlers
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	"github.com/mchus/quoteforge/internal/repository"
+	"github.com/mchus/quoteforge/internal/services"
+)
+
+type ComponentHandler struct {
+	componentService *services.ComponentService
+}
+
+func NewComponentHandler(componentService *services.ComponentService) *ComponentHandler {
+	return &ComponentHandler{componentService: componentService}
+}
+
+func (h *ComponentHandler) List(c *gin.Context) {
+	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
+	perPage, _ := strconv.Atoi(c.DefaultQuery("per_page", "20"))
+
+	filter := repository.ComponentFilter{
+		Category: c.Query("category"),
+		Vendor:   c.Query("vendor"),
+		Search:   c.Query("search"),
+		HasPrice: c.Query("has_price") == "true",
+	}
+
+	result, err := h.componentService.List(filter, page, perPage)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, result)
+}
+
+func (h *ComponentHandler) Get(c *gin.Context) {
+	lotName := c.Param("lot_name")
+
+	component, err := h.componentService.GetByLotName(lotName)
+	if err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "component not found"})
+		return
+	}
+
+	c.JSON(http.StatusOK, component)
+}
+
+func (h *ComponentHandler) GetCategories(c *gin.Context) {
+	categories, err := h.componentService.GetCategories()
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, categories)
+}
+
+func (h *ComponentHandler) GetVendors(c *gin.Context) {
+	category := c.Query("category")
+
+	vendors, err := h.componentService.GetVendors(category)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, vendors)
+}