feat(phase2): per-board access control UI

- BoardAccessControl component with user/group autocomplete
- BoardShareDialog modal with copy link, guest toggle, quick add
- Board permissions REST API (GET/POST/DELETE)
- Access indicators on BoardCard (lock, globe, shared icons)
- Guest access toggle in board editor with status preview
- Enhanced PermissionEditor with search autocomplete
- i18n translations for all new strings (EN/RU)

src/lib/i18n/en.json

@@ -52,6 +52,25 @@
   "board.creating": "Creating...",
   "board.default_board": "Default board",
   "board.guest_accessible": "Guest accessible",
+  "board.guest_access_title": "Guest Access",
+  "board.guest_access_description": "When enabled, this board is visible to unauthenticated visitors without requiring sign-in.",
+  "board.guest_access_enabled": "This board is publicly accessible",
+  "board.guest_access_disabled": "This board is private",
+  "board.permissions_title": "Permissions",
+  "board.permissions_description": "Manage who can view, edit, or administer this board.",
+  "board.access_grant": "Grant Access",
+  "board.access_search_placeholder": "Search...",
+  "board.access_loading": "Loading permissions...",
+  "board.access_none": "No permissions configured for this board.",
+  "board.access_private": "Private",
+  "board.access_shared": "Shared",
+  "board.share": "Share",
+  "board.share_title": "Share \"{name}\"",
+  "board.share_copy_link": "Copy Link",
+  "board.share_copied": "Copied!",
+  "board.share_guest_description": "Anyone with the link can view this board without signing in.",
+  "board.share_add_access": "Add People or Groups",
+  "board.share_current_access": "Current Access",
 
   "section.title_label": "Title",
   "section.icon_label": "Icon",
@@ -192,6 +211,7 @@
   "admin.perm_level_column": "Level",
   "admin.perm_action_column": "Action",
   "admin.perm_none": "No permissions configured.",
+  "admin.perm_search_placeholder": "Type to search...",
 
   "search.placeholder": "Search apps and boards...",
   "search.trigger": "Search...",