v0.6: template-manager owns the product catalog

The host no longer carries a runtime product catalog. products.js
shrinks to a legacy single-product stub; the canonical catalog lives in
template-manager's productsStore, seeded ONCE on first boot from the
new seedProducts.js (after that the store under templates/ is
authoritative and the seed is ignored — intentional, so restarts never
rewrite an admin-managed catalog). phoneModels.js and
templateCategories.js are the supporting constant sets, and
docs/template-schema.md documents the v4 schema.

templates/ is the admin-managed store itself (_products_index.json +
products/<id>/product.json, JSON only) — committed so the configured
catalog (sizes, pricing, options built up in the admin UI) survives a
fresh checkout rather than regressing to the seed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

templates/products/1ed028ad-1998-4ace-813b-79023bd08c1d/product.json

@@ -0,0 +1,35 @@
+{
+  "id": "1ed028ad-1998-4ace-813b-79023bd08c1d",
+  "slug": "notebook",
+  "label": "Notebook",
+  "description": "A5 hardcover notebook, 120 lined pages.",
+  "category": "Stationery",
+  "options": [],
+  "sizes": [
+    {
+      "id": "add070b4-1fa3-47bb-84a5-df8d99c2b821",
+      "slug": "a5",
+      "label": "A5",
+      "physical": {
+        "width": 5.5,
+        "height": 8.5,
+        "unit": "in"
+      },
+      "canvas": {
+        "width": 550,
+        "height": 850
+      },
+      "printZone": {
+        "x": 55,
+        "y": 85,
+        "width": 440,
+        "height": 680
+      },
+      "silhouettePath": "M22,0 L528,0 A22,22 0 0 1 550,22 L550,828 A22,22 0 0 1 528,850 L22,850 A22,22 0 0 1 0,828 L0,22 A22,22 0 0 1 22,0 Z",
+      "mockupFallbackColor": "#fafaf9",
+      "basePriceCents": 1500
+    }
+  ],
+  "createdAt": "2026-05-25T12:31:21.559Z",
+  "updatedAt": "2026-05-25T12:31:21.559Z"
+}