feat: P2.3 Folder Sharing + P2.5 Email Import + P2.6 Contact Import + P2.7 Free/Busy

- P2.3: Folder sharing system — ShareFolderDialog, sharing-store, sharing-settings
- P2.5: Email import (.eml, .tgz, .zip) with dedup and progress
- P2.6: Contact import (vCard + CSV) with auto-mapping
- P2.7: Free/Busy view grid with color-coded slots

locales/en/common.json

@@ -892,6 +892,8 @@
       "downloads": "Downloads",
       "content_senders": "Content & Senders",
       "about_data": "About & Data",
+      "import": "Import",
+      "sharing": "Sharing",
       "debug": "Debug"
     },
     "tab_groups": {
@@ -2057,6 +2059,7 @@
     "new_subfolder": "New subfolder...",
     "new_folder": "New folder...",
     "rename": "Rename...",
+    "share_folder": "Share Folder...",
     "import_email": "Import .eml or .zip...",
     "empty_folder": "Empty folder",
     "empty_folder_generic": "Empty folder",
@@ -2662,6 +2665,20 @@
       "no_participants": "No participants",
       "count": "{count, plural, one {# participant} other {# participants}}"
     },
+    "freeBusy": {
+      "title": "Availability",
+      "check": "Check Availability",
+      "hide": "Hide Availability",
+      "loading": "Loading...",
+      "no_participants": "Add participants to check availability.",
+      "timezone": "Timezone",
+      "free": "Free",
+      "busy": "Busy",
+      "tentative": "Tentative",
+      "unavailable": "Out of office",
+      "unknown": "No information",
+      "click_to_select": "Click a free slot to select this time"
+    },
     "recurrence": {
       "title": "Recurrence",
       "none": "Does not repeat",
@@ -3012,7 +3029,14 @@
       "readWrite": "Read & write",
       "manager": "Manager",
       "custom": "Custom"
-    }
+    },
+    "tab_shared_by_me": "Shared by me",
+    "tab_shared_with_me": "Shared with me",
+    "no_shares_by_me": "You haven't shared anything yet.",
+    "no_shares_with_me": "No folders shared with you yet.",
+    "shared_by": "Shared by",
+    "accept": "Accept",
+    "decline": "Decline"
   },
   "advanced_search": {
     "title": "Advanced Search",