feat: restructure UI with tab-based navigation (#119)

Reorganizes the merchant dashboard into a tab-based layout:
- Tabs: Merchant | Shipping | Stalls | Products | Messages | Orders
- Publish dropdown with NIP-15 options (NIP-99 disabled/coming soon)
- Consistent UI patterns across all tabs:
  - Search/filter/buttons aligned right
  - Actions column on right side of tables
  - Equal-width tabs
- Stalls tab: popup edit dialog, navigation to Products/Orders
- Products tab: filter icon dropdown for stall filtering
- Modular component structure for each tab section
- Fixed product API calls to use correct endpoints

Closes #119

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

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

static/components/merchant-tab.js

@@ -0,0 +1,37 @@
+window.app.component('merchant-tab', {
+  name: 'merchant-tab',
+  template: '#merchant-tab',
+  delimiters: ['${', '}'],
+  props: [
+    'merchant-id',
+    'inkey',
+    'adminkey',
+    'show-keys',
+    'merchant-active',
+    'public-key',
+    'private-key',
+    'is-admin'
+  ],
+  computed: {
+    marketClientUrl: function () {
+      return '/nostrmarket/market'
+    }
+  },
+  methods: {
+    toggleShowKeys: function () {
+      this.$emit('toggle-show-keys')
+    },
+    hideKeys: function () {
+      this.$emit('hide-keys')
+    },
+    handleMerchantDeleted: function () {
+      this.$emit('merchant-deleted')
+    },
+    toggleMerchantState: function () {
+      this.$emit('toggle-merchant-state')
+    },
+    restartNostrConnection: function () {
+      this.$emit('restart-nostr-connection')
+    }
+  }
+})