feat: tags, unpublish and image upload for the author

- GET /_bm/api/v1/tags: the jz_bm_tags dictionary, to material managers
- POST /materials/{id}/unpublish: back to drafts, no revision bump, the
  search document resynced
- POST /materials/{id}/images: one JPEG/PNG/GIF/WebP per request through
  storeMaterialUpload, refusals with reason type, size or count
- storeMaterialUpload/fileRefusalFor: attach.ErrNotImage is a type
  refusal, not a 500; storeMaterialFile keeps its texts
- the author's routes get their own per-user buckets (the inline
  throttle form shares one counter per user)
- README: the author routes and revision on the student detail

controllers/api/material_edit_test.go

@@ -1,8 +1,12 @@
 package api
 
 import (
+	"errors"
+	"fmt"
 	"strings"
 	"testing"
+
+	"git.golem15.com/golem15/summercms/modules/lagoon/attach"
 )
 
 const fullEditBody = `{"revision":3,"title":"Notatka","type":"notatka","body":"Tekst","source":null,"url":null,"meeting_id":null,"tags":["lektura"]}`
@@ -144,3 +148,37 @@ func TestNormalizeBody(t *testing.T) {
 		}
 	}
 }
+
+// TestFileRefusalReasons checks how attach.Store errors become refusals of
+// the material file routes: size for ErrTooLarge, type for ErrFileType,
+// ErrMIMEType and the image-mode ErrNotImage (no longer a 500), and no
+// refusal for other errors.
+func TestFileRefusalReasons(t *testing.T) {
+	cases := []struct {
+		err    error
+		reason string
+	}{
+		{attach.ErrTooLarge, "size"},
+		{attach.ErrFileType, "type"},
+		{attach.ErrMIMEType, "type"},
+		{attach.ErrNotImage, "type"},
+		{fmt.Errorf("store: %w", attach.ErrNotImage), "type"},
+	}
+	for _, tc := range cases {
+		why, ok := fileRefusalFor(tc.err, "a.png", imageLimits)
+		if !ok || why.Reason != tc.reason || !strings.HasPrefix(why.Text, "a.png: ") {
+			t.Errorf("fileRefusalFor(%v) = %+v %v, want reason %s", tc.err, why, ok, tc.reason)
+		}
+	}
+	if why, _ := fileRefusalFor(attach.ErrTooLarge, "a.png", imageLimits); why.Text != "a.png: the file is larger than 50 MB." {
+		t.Errorf("size text = %q", why.Text)
+	}
+	for _, err := range []error{nil, errors.New("disk full")} {
+		if why, ok := fileRefusalFor(err, "a.png", imageLimits); ok {
+			t.Errorf("fileRefusalFor(%v) = %+v, want no refusal", err, why)
+		}
+	}
+	if !imageLimits.Image || imageLimits.MaxBytes != MaterialFileMaxBytes {
+		t.Errorf("imageLimits = %+v", imageLimits)
+	}
+}