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

src/i18n/en.json

@@ -459,6 +459,52 @@
     "global.locked": "Locked",
     "global.unlocked": "Unlocked",
     "global.confirm": "Confirm",
+    "global.equipment": "Equipment",
+    "equipment.title": "Equipment",
+    "equipment.createItem": "Create Equipment",
+    "equipment.createItemTitle": "Create Equipment",
+    "equipment.editItemTitle": "Edit Equipment",
+    "equipment.name": "Name",
+    "equipment.namePlaceholder": "Enter equipment name...",
+    "equipment.type": "Type",
+    "equipment.stats": "Stats",
+    "equipment.description": "Description",
+    "equipment.descriptionPlaceholder": "Enter description (optional)...",
+    "equipment.emptySlot": "Empty",
+    "equipment.unequip": "Unequip",
+    "equipment.equip": "Equip",
+    "equipment.editItem": "Edit item",
+    "equipment.deleteItem": "Delete item",
+    "equipment.inventoryTitle": "Inventory",
+    "equipment.slots.helmet": "Helmet",
+    "equipment.slots.necklace": "Necklace",
+    "equipment.slots.bodyArmor": "Body Armor",
+    "equipment.slots.gloves": "Gloves",
+    "equipment.slots.pants": "Pants",
+    "equipment.slots.shoes": "Shoes",
+    "equipment.slots.ring1": "Ring 1",
+    "equipment.slots.ring2": "Ring 2",
+    "equipment.slots.ring3": "Ring 3",
+    "equipment.slots.ring4": "Ring 4",
+    "equipment.slots.ring5": "Ring 5",
+    "equipment.slots.ring6": "Ring 6",
+    "equipment.slots.ring7": "Ring 7",
+    "equipment.slots.ring8": "Ring 8",
+    "equipment.slots.ring9": "Ring 9",
+    "equipment.slots.ring10": "Ring 10",
+    "equipment.slots.accessory1": "Accessory 1",
+    "equipment.slots.accessory2": "Accessory 2",
+    "equipment.slots.accessory3": "Accessory 3",
+    "equipment.types.helmet": "Helmet",
+    "equipment.types.necklace": "Necklace",
+    "equipment.types.bodyArmor": "Body Armor",
+    "equipment.types.gloves": "Gloves",
+    "equipment.types.pants": "Pants",
+    "equipment.types.shoes": "Shoes",
+    "equipment.types.ring": "Ring",
+    "equipment.types.accessory": "Accessory",
+    "template.settingsModal.display.showEquipment": "Show Equipment",
+    "template.settingsModal.display.showEquipmentNote": "Manage equipped gear and stat bonuses from items.",
     "inventory.addItemPlaceholder": "Enter item name...",
     "inventory.stored.removeLocationConfirm": "Remove \"{location}\"? This will delete all items stored there.",
     "userStats.clickToEdit": "Click to edit",