frontend: fix message file attach + make shared appointments clickable

- replace the attach "+" menu (whose programmatic fileInput.click() was dropped
  by user-activation gating, so files never attached and no chip appeared) with
  a native <label> paperclip + a direct appointment button
- shared-appointment cards are now clickable for both parties, opening an
  AppointmentDetailDialog with the full snapshot (when/type/provider/patient/status)

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

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

@@ -705,7 +705,13 @@
       "apptSearchPlaceholder": "Patient name…",
       "apptNoMatches": "No appointments match.",
       "apptEmpty": "No appointments yet.",
-      "apptCardLabel": "Appointment"
+      "apptCardLabel": "Appointment",
+      "apptDetailTitle": "Appointment details",
+      "apptWhen": "When",
+      "apptType": "Type",
+      "apptProvider": "Provider",
+      "apptPatient": "Patient",
+      "apptStatus": "Status"
     }
   },
   "analysis": {