refactor: DRY layout bounds via --page-max-width and --sidebar-width CSS vars
Add --page-max-width (1200px), --page-padding-x (1rem), and --sidebar-width (260px)
to theme.css so all views share a single source of truth.
- HomeView: 1100px → var(--page-max-width) (aligns with all other views)
- NotesListView, TasksListView, ProjectListView, ProjectView, CalendarView: var(--page-max-width)
- ChatView: sidebar + context sidebar → var(--sidebar-width); inner message/input
column max-widths → var(--page-max-width)
- KnowledgeView: filter panel 180px → var(--sidebar-width); minichat left offset updated
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>