feat: add categories admin UI with CRUD

Wire up categories service, add CategoriesHandler with full CRUD, create index/edit templates, register routes in server.go, and add Categories nav link.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

handlers/categories.go

@@ -0,0 +1,101 @@
+package handlers
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/gofiber/fiber/v3"
+	"lmika.dev/lmika/weiro/models"
+	"lmika.dev/lmika/weiro/services/categories"
+)
+
+type CategoriesHandler struct {
+	CategoryService *categories.Service
+}
+
+func (ch CategoriesHandler) Index(c fiber.Ctx) error {
+	cats, err := ch.CategoryService.ListCategoriesWithCounts(c.Context())
+	if err != nil {
+		return err
+	}
+
+	return c.Render("categories/index", fiber.Map{
+		"categories": cats,
+	})
+}
+
+func (ch CategoriesHandler) New(c fiber.Ctx) error {
+	cat := models.Category{
+		GUID: models.NewNanoID(),
+	}
+	return c.Render("categories/edit", fiber.Map{
+		"category": cat,
+		"isNew":    true,
+	})
+}
+
+func (ch CategoriesHandler) Edit(c fiber.Ctx) error {
+	catID, err := strconv.ParseInt(c.Params("categoryID"), 10, 64)
+	if err != nil {
+		return fiber.ErrBadRequest
+	}
+
+	cat, err := ch.CategoryService.GetCategory(c.Context(), catID)
+	if err != nil {
+		return err
+	}
+
+	return c.Render("categories/edit", fiber.Map{
+		"category": cat,
+		"isNew":    false,
+	})
+}
+
+func (ch CategoriesHandler) Create(c fiber.Ctx) error {
+	var req categories.CreateCategoryParams
+	if err := c.Bind().Body(&req); err != nil {
+		return err
+	}
+
+	_, err := ch.CategoryService.CreateCategory(c.Context(), req)
+	if err != nil {
+		return err
+	}
+
+	site := models.MustGetSite(c.Context())
+	return c.Redirect().To(fmt.Sprintf("/sites/%v/categories", site.ID))
+}
+
+func (ch CategoriesHandler) Update(c fiber.Ctx) error {
+	catID, err := strconv.ParseInt(c.Params("categoryID"), 10, 64)
+	if err != nil {
+		return fiber.ErrBadRequest
+	}
+
+	var req categories.CreateCategoryParams
+	if err := c.Bind().Body(&req); err != nil {
+		return err
+	}
+
+	_, err = ch.CategoryService.UpdateCategory(c.Context(), catID, req)
+	if err != nil {
+		return err
+	}
+
+	site := models.MustGetSite(c.Context())
+	return c.Redirect().To(fmt.Sprintf("/sites/%v/categories", site.ID))
+}
+
+func (ch CategoriesHandler) Delete(c fiber.Ctx) error {
+	catID, err := strconv.ParseInt(c.Params("categoryID"), 10, 64)
+	if err != nil {
+		return fiber.ErrBadRequest
+	}
+
+	if err := ch.CategoryService.DeleteCategory(c.Context(), catID); err != nil {
+		return err
+	}
+
+	site := models.MustGetSite(c.Context())
+	return c.Redirect().To(fmt.Sprintf("/sites/%v/categories", site.ID))
+}