feat(chat): file attachments as chips, CoT closed, AI add-to-inventory

Chat fixes (#1/#6/#7):
- chat-input passes raw File[] up instead of inlining file text
- chat-panel sends files as FileUIPart and renders them with the
  ai-elements Attachments component (no more raw text dumps)
- backend extracts text-like file content for the model in routes/chat
- Chain-of-Thought now defaults to collapsed
- file upload works regardless of whether the input has text

AI add-to-inventory (#2):
- new proposeInventory tool (validates items, streams an approval card)
- system prompt distinguishes stocking inventory vs. billing a patient
- ActionPreviewCard commits inventory via POST /api/inventory

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/ai-chat.ts

@@ -56,7 +56,8 @@ export type ActionPreviewKind =
   | "appointment"
   | "task"
   | "prescription"
-  | "invoice";
+  | "invoice"
+  | "inventory";
 export type ActionPreviewData = {
   token: string;
   kind: ActionPreviewKind;

frontend/lib/i18n/locales/en/translation.json

@@ -795,7 +795,8 @@
     },
     "queue": {
       "label": "Queued · {{count}}",
-      "remove": "Remove from queue"
+      "remove": "Remove from queue",
+      "attachmentsOnly": "{{count}} attachment(s)"
     },
     "veil": {
       "title": "Veil",
@@ -810,14 +811,17 @@
         "appointment": "Proposed appointment",
         "task": "Proposed task",
         "prescription": "Proposed prescription",
-        "invoice": "Proposed invoice"
+        "invoice": "Proposed invoice",
+        "inventory": "Proposed inventory"
       },
       "kind": {
         "appointment": "Appointment added.",
         "task": "Task added.",
         "prescription": "Prescription added.",
-        "invoice": "Invoice added."
+        "invoice": "Invoice added.",
+        "inventory": "Inventory updated."
       },
+      "inventoryItems": "{{count}} item(s)",
       "approve": "Add",
       "adding": "Adding…",
       "discard": "Discard",