Fix TUI bugs: folder selection, filter stability, UI consistency

- Mail: Fix folder/account selector not triggering reload (use direct
  fetch instead of reactive reload_needed flag)
- Tasks: Store all_projects/all_tags on mount so filters don't change
  when filtering; add OR search for multiple tags
- Sync: Use rounded borders and border_title for sidebar/activity log
- Calendar: Remove padding from mini-calendar, add rounded border and
  border_title to invites panel

src/tasks/app.py

@@ -197,6 +197,8 @@ class TasksApp(App):
         self.tasks = []
         self.projects = []
         self.tags = []
+        self.all_projects = []  # Stable list of all projects (not filtered)
+        self.all_tags = []  # Stable list of all tags (not filtered)
         self.current_project_filter = None
         self.current_tag_filters = []
         self.current_sort_column = "priority"
@@ -261,7 +263,10 @@ class TasksApp(App):
             height = max(10, min(90, height))
             notes_pane.styles.height = f"{height}%"
 
-        # Load tasks (this will also update the sidebar)
+        # Load ALL projects and tags once for stable sidebar
+        self._load_all_filters()
+
+        # Load tasks (filtered by current filters)
         self.load_tasks()
 
     def _setup_columns(self, table: DataTable, columns: list[str]) -> None:
@@ -375,32 +380,58 @@ class TasksApp(App):
         if not self.backend:
             return
 
-        # Get tasks with current filters
-        self.tasks = self.backend.get_tasks(
-            project=self.current_project_filter,
-            tags=self.current_tag_filters if self.current_tag_filters else None,
-        )
+        # Get ALL tasks first (unfiltered)
+        all_tasks = self.backend.get_tasks()
+
+        # Apply client-side filtering for OR logic
+        self.tasks = self._filter_tasks(all_tasks)
 
         # Sort tasks
         self._sort_tasks()
 
-        # Also load projects and tags for filtering
-        self.projects = self.backend.get_projects()
-        self.tags = self.backend.get_tags()
-
-        # Update sidebar with available filters
-        self._update_sidebar()
-
         # Update table
         self._update_table()
 
+    def _load_all_filters(self) -> None:
+        """Load all projects and tags once for stable sidebar."""
+        if not self.backend:
+            return
+
+        self.all_projects = self.backend.get_projects()
+        self.all_tags = self.backend.get_tags()
+
+        # Update sidebar with stable filter options
+        self._update_sidebar()
+
+    def _filter_tasks(self, tasks: list[Task]) -> list[Task]:
+        """Filter tasks by current project and tag filters using OR logic.
+
+        - If project filter is set, only show tasks from that project
+        - If tag filters are set, show tasks that have ANY of the selected tags (OR)
+        """
+        filtered = tasks
+
+        # Filter by project (single project filter is AND)
+        if self.current_project_filter:
+            filtered = [t for t in filtered if t.project == self.current_project_filter]
+
+        # Filter by tags using OR logic - show tasks with ANY of the selected tags
+        if self.current_tag_filters:
+            filtered = [
+                t
+                for t in filtered
+                if any(tag in t.tags for tag in self.current_tag_filters)
+            ]
+
+        return filtered
+
     def _update_sidebar(self) -> None:
-        """Update the filter sidebar with current projects and tags."""
+        """Update the filter sidebar with all available projects and tags."""
         try:
             sidebar = self.query_one("#sidebar", FilterSidebar)
-            # Convert projects to (name, count) tuples
-            project_data = [(p.name, p.task_count) for p in self.projects if p.name]
-            sidebar.update_filters(projects=project_data, tags=self.tags)
+            # Use stable all_projects/all_tags, not filtered ones
+            project_data = [(p.name, p.task_count) for p in self.all_projects if p.name]
+            sidebar.update_filters(projects=project_data, tags=self.all_tags)
         except Exception:
             pass  # Sidebar may not be mounted yet