Fix category filter bug and add tab accessibility

The category tabs were not filtering because the generic tab event handler
was overwriting currentFilter with undefined (category tabs use data-category
not data-filter). Fixed by targeting only [data-filter] tabs and clearing
categoryFilter when switching to non-category tabs.

Added proper ARIA attributes for screen reader accessibility:
- role="tablist" on nav-tabs container
- role="tab" and aria-selected on all tab buttons
- Dynamic aria-selected updates on tab clicks

Also includes API support for category field and deploy script update.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

categories.json

@@ -0,0 +1,26 @@
+{
+    "flours": {
+        "name": "Flours & Starches",
+        "color": "#8B4513"
+    },
+    "spices": {
+        "name": "Spices & Seasonings",
+        "color": "#CD853F"
+    },
+    "pasta": {
+        "name": "Pasta & Grains",
+        "color": "#DAA520"
+    },
+    "baking": {
+        "name": "Baking",
+        "color": "#D2691E"
+    },
+    "produce": {
+        "name": "Beans & Dried Produce",
+        "color": "#556B2F"
+    },
+    "other": {
+        "name": "Other",
+        "color": "#708090"
+    }
+}