Add post image upload interface (#12)

Adds accessible drag-and-drop and browse controls, staged attachment editing, responsive lazy-loaded thread image grids, and UI regression coverage.

Reviewed-on: #12
Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/web/server.go

@@ -104,6 +104,11 @@ type threadPostCtx struct {
 	Depth int
 }
 
+type imagePickerCtx struct {
+	ID     string
+	Images []store.PostImage
+}
+
 func New(st store.Store, sessionStore scs.Store, templateFS fs.FS, staticFS fs.FS, cfg Config) (*Server, error) {
 	if cfg.Blob == nil {
 		cfg.Blob = blob.Disabled{}
@@ -118,6 +123,12 @@ func New(st store.Store, sessionStore scs.Store, templateFS fs.FS, staticFS fs.F
 		"postCtx": func(user *store.User, csrf string, root, post *store.Post, depth int) threadPostCtx {
 			return threadPostCtx{User: user, CSRF: csrf, Root: root, Post: post, Depth: depth}
 		},
+		"imagePicker": func(id string, images []store.PostImage) imagePickerCtx {
+			return imagePickerCtx{ID: id, Images: images}
+		},
+		"newImagePicker": func(id string) imagePickerCtx {
+			return imagePickerCtx{ID: id}
+		},
 		"add":         func(a, b int) int { return a + b },
 		"rank":        func(i int) int { return i + 1 },
 		"isAdmin":     func(u *store.User) bool { return u.Admin() },