Add tabbed sub-views to bins section, create-bin-from-source flow

Bins section now mirrors the grids section with two tabs:
- Bins: gallery of processed bin records
- Sources: source images tagged with uses=['bin'], with upload and
  '+ Bin' button to create a bin record from an existing source image

Server: POST /api/bins/from-source accepts source_id, creates bin
record and adds 'bin' to the source image's uses array.

URL state: /bins → bins tab, /bins/sources → sources tab.

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

server.mjs

@@ -662,6 +662,40 @@ app.get('/api/bins/:id', (req, res) => {
 	ok(res, { bin });
 });
 
+// Create a bin from an already-uploaded source image
+app.post('/api/bins/from-source', (req, res) => {
+	const { source_id, name = '' } = req.body;
+	if (!source_id) return fail(res, 'source_id is required');
+	const src = get_source_image(source_id);
+	if (!src) return fail(res, 'source image not found', 404);
+
+	// Add 'bin' to uses if not already there
+	if (!src.uses?.includes('bin')) {
+		add_source_image({ ...src, uses: [...(src.uses ?? []), 'bin'] });
+	}
+
+	const mx = Math.round(src.width  * 0.15);
+	const my = Math.round(src.height * 0.15);
+	const bin = {
+		id: generate_id(),
+		name: name.trim() || src.original_name?.replace(/\.[^.]+$/, '') || 'Bin',
+		source_id,
+		source_w: src.width,
+		source_h: src.height,
+		corners: [
+			{ x: mx,            y: my             },
+			{ x: src.width - mx, y: my             },
+			{ x: src.width - mx, y: src.height - my },
+			{ x: mx,            y: src.height - my },
+		],
+		image_filename: null,
+		created_at: Date.now(),
+		updated_at: Date.now(),
+	};
+	set_bin(bin);
+	ok(res, { bin });
+});
+
 // Upload a source image for a bin and create the bin record (no processing yet)
 app.post('/api/bins', upload.single('image'), async (req, res) => {
 	if (!req.file) return fail(res, 'no image uploaded');