feat: add Equipment tab with slot-type validation

Add a new Equipment tab to manage player gear and stat bonuses.

Features:
- 19 equipment slots across 8 categories (helmet, necklace, body armor, gloves, pants, shoes, rings, accessories)
- Type-to-slot validation: each type has max equipped limits (1 helmet, 10 rings, 3 accessories, etc.)
- Auto-slot assignment: equipping a ring fills the first available ring slot
- Stat bonuses from equipped items display on RPG attributes (e.g. STR 10 +2)
- Create/edit modal with stat checkboxes per RPG attribute
- Inventory list for unequipped items

Architecture:
- Shared constants in src/systems/equipment/constants.js
- Category-based types (Ring, Accessory) with auto-slot assignment
- v7 migration converts legacy slot-specific types to generic categories
- Full i18n support for all UI strings

Files:
- New: src/systems/equipment/constants.js
- New: src/systems/interaction/equipmentActions.js
- New: src/systems/rendering/equipment.js
- Modified: state.js, persistence.js, template.html, index.js
- Modified: userStats.js, desktop.js, mobile.js, layout.js, modals.js
- Modified: apiClient.js, sillytavern.js, style.css, en.json

template.html

@@ -96,6 +96,14 @@
                 <!-- Divider after Inventory -->
                 <div id="rpg-divider-inventory" class="rpg-divider"></div>
 
+                <!-- Equipment Section -->
+                <div id="rpg-equipment" class="rpg-section rpg-equipment-section">
+                    <!-- Content will be populated by JavaScript -->
+                </div>
+
+                <!-- Divider after Equipment -->
+                <div id="rpg-divider-equipment" class="rpg-divider"></div>
+
                 <!-- Quests Section -->
                 <div id="rpg-quests" class="rpg-section rpg-quests-section">
                     <!-- Content will be populated by JavaScript -->
@@ -448,6 +456,15 @@
                     Track items carried, clothing worn, stored items, and assets.
                 </small>
 
+                <label class="checkbox_label">
+                    <input type="checkbox" id="rpg-toggle-equipment" />
+                    <span data-i18n-key="template.settingsModal.display.showEquipment">Show Equipment</span>
+                </label>
+                <small style="display: block; margin-left: 24px; margin-top: -8px; color: #888; font-size: 11px;"
+                    data-i18n-key="template.settingsModal.display.showEquipmentNote">
+                    Manage equipped gear and stat bonuses from items.
+                </small>
+
                 <label class="checkbox_label">
                     <input type="checkbox" id="rpg-toggle-quests" />
                     <span data-i18n-key="template.settingsModal.display.showQuests">Show Quests</span>