feat: add EditEventScreen with calendar and chat mode support

Add a unified event editor that works in two modes:
- Calendar mode: Create/edit events directly via EventService API
- Chat mode: Edit AI-proposed events before confirming them

The chat mode allows users to modify proposed events (title, time,
recurrence) and persists changes both locally and to the server.

New components: DateTimePicker, ScrollableDropdown, useDropdownPosition
New API: PUT /api/chat/messages/:messageId/proposal

package-lock.json

@@ -23,6 +23,7 @@
       "dependencies": {
         "@calchat/shared": "*",
         "@expo/vector-icons": "^15.0.3",
+        "@react-native-community/datetimepicker": "8.4.4",
         "@react-navigation/bottom-tabs": "^7.4.0",
         "@react-navigation/elements": "^2.6.3",
         "@react-navigation/native": "^7.1.8",
@@ -52,6 +53,7 @@
         "react-native-screens": "~4.16.0",
         "react-native-web": "~0.21.0",
         "react-native-worklets": "0.5.1",
+        "rrule": "^2.8.1",
         "zustand": "^5.0.9"
       },
       "devDependencies": {
@@ -2647,6 +2649,29 @@
         }
       }
     },
+    "node_modules/@react-native-community/datetimepicker": {
+      "version": "8.4.4",
+      "resolved": "https://registry.npmjs.org/@react-native-community/datetimepicker/-/datetimepicker-8.4.4.tgz",
+      "integrity": "sha512-bc4ZixEHxZC9/qf5gbdYvIJiLZ5CLmEsC3j+Yhe1D1KC/3QhaIfGDVdUcid0PdlSoGOSEq4VlB93AWyetEyBSQ==",
+      "license": "MIT",
+      "dependencies": {
+        "invariant": "^2.2.4"
+      },
+      "peerDependencies": {
+        "expo": ">=52.0.0",
+        "react": "*",
+        "react-native": "*",
+        "react-native-windows": "*"
+      },
+      "peerDependenciesMeta": {
+        "expo": {
+          "optional": true
+        },
+        "react-native-windows": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/@react-native/assets-registry": {
       "version": "0.81.5",
       "license": "MIT",
@@ -10537,6 +10562,8 @@
     },
     "node_modules/rrule": {
       "version": "2.8.1",
+      "resolved": "https://registry.npmjs.org/rrule/-/rrule-2.8.1.tgz",
+      "integrity": "sha512-hM3dHSBMeaJ0Ktp7W38BJZ7O1zOgaFEsn41PDk+yHoEtfLV+PoJt9E9xAlZiWgf/iqEqionN0ebHFZIDAp+iGw==",
       "license": "BSD-3-Clause",
       "dependencies": {
         "tslib": "^2.4.0"