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/cb43b749-05c0-4d1c-8d0b-dadd9b28574d/product.json

@@ -0,0 +1,35 @@
+{
+  "id": "cb43b749-05c0-4d1c-8d0b-dadd9b28574d",
+  "slug": "hat",
+  "label": "Hat",
+  "description": "Adjustable baseball cap with embroidered front print.",
+  "category": "Apparel",
+  "options": [],
+  "sizes": [
+    {
+      "id": "778c4b47-a46b-4753-8fa2-be8af1523f4a",
+      "slug": "cap",
+      "label": "Baseball Cap",
+      "physical": {
+        "width": 5,
+        "height": 2,
+        "unit": "in"
+      },
+      "canvas": {
+        "width": 500,
+        "height": 200
+      },
+      "printZone": {
+        "x": 50,
+        "y": 20,
+        "width": 400,
+        "height": 160
+      },
+      "silhouettePath": "M30,0 L470,0 A30,30 0 0 1 500,30 L500,170 A30,30 0 0 1 470,200 L30,200 A30,30 0 0 1 0,170 L0,30 A30,30 0 0 1 30,0 Z",
+      "mockupFallbackColor": "#fce7f3",
+      "basePriceCents": 2200
+    }
+  ],
+  "createdAt": "2026-05-25T12:31:21.562Z",
+  "updatedAt": "2026-05-25T12:31:21.562Z"
+}