Add Obsidian vault import feature (#8)

- New 'Import Obsidian' action on site settings page
- Upload a zip file of an Obsidian vault to import all notes as posts
- Markdown notes imported with title from filename, published date from
  file timestamp, and body with front-matter stripped
- Images and other attachments saved as Upload records
- New obsimport service handles zip traversal and import logic
- Unit tests for front-matter stripping

Co-authored-by: Shelley <shelley@exe.dev>

Co-authored-by: exe.dev user <exedev@kernel-leviathan.exe.xyz>
Reviewed-on: #8

handlers/obsimport.go

@@ -0,0 +1,50 @@
+package handlers
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/gofiber/fiber/v3"
+	"lmika.dev/lmika/weiro/models"
+	"lmika.dev/lmika/weiro/services/obsimport"
+)
+
+type ObsImportHandler struct {
+	ObsImportService *obsimport.Service
+	ScratchDir       string
+}
+
+func (h ObsImportHandler) Form(c fiber.Ctx) error {
+	return c.Render("obsimport/form", fiber.Map{})
+}
+
+func (h ObsImportHandler) Upload(c fiber.Ctx) error {
+	site := c.Locals("site").(models.Site)
+
+	fileHeader, err := c.FormFile("zipfile")
+	if err != nil {
+		return fiber.NewError(fiber.StatusBadRequest, "no file provided")
+	}
+
+	// Save uploaded file to scratch dir
+	if err := os.MkdirAll(h.ScratchDir, 0755); err != nil {
+		return err
+	}
+
+	dstPath := filepath.Join(h.ScratchDir, models.NewNanoID()+".zip")
+	if err := c.SaveFile(fileHeader, dstPath); err != nil {
+		return err
+	}
+	defer os.Remove(dstPath)
+
+	result, err := h.ObsImportService.ImportZip(c.Context(), dstPath)
+	if err != nil {
+		return err
+	}
+
+	return c.Render("obsimport/result", fiber.Map{
+		"result":  result,
+		"siteURL": fmt.Sprintf("/sites/%v/posts", site.ID),
+	})
+}