Make bin editor open to image view; corners editing on demand

- Default view: processed image (full size in dialog), or placeholder if
  not yet processed. Name and type selector always visible at top.
- "Adjust corners…" button reveals the canvas editor (lazy-loaded on
  first click, so there's no canvas allocation cost on open).
- "← Back to image" returns to the image view.
- Corners are only re-processed on Save if the canvas was opened.
- Tabs reduced to Fields | Contents (Corners is no longer a tab).
- Added preview image CSS; btn-link style for the back button.

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

public/style.css

@@ -1988,6 +1988,46 @@ nav {
 	margin-left: 0.25rem;
 }
 
+.bin-editor-preview-wrap {
+	width: 100%;
+	background: #0e0e0e;
+	border-radius: 4px;
+	display: flex;
+	align-items: center;
+	justify-content: center;
+	min-height: 120px;
+	margin-bottom: 0.5rem;
+	overflow: hidden;
+}
+
+.bin-editor-preview-img {
+	max-width: 100%;
+	max-height: 55vh;
+	display: block;
+	object-fit: contain;
+}
+
+.bin-editor-no-image {
+	color: var(--text-faint);
+	font-size: 0.85rem;
+	padding: 2rem;
+	text-align: center;
+}
+
+.btn-link {
+	background: none;
+	border: none;
+	color: var(--text-muted);
+	cursor: pointer;
+	font-size: 0.8rem;
+	padding: 0.25rem 0;
+	text-decoration: underline;
+}
+
+.btn-link:hover {
+	color: var(--text);
+}
+
 .bin-editor-canvas {
 	display: block;
 	border-radius: 4px;