Every other navigation entry in the user menu (Settings, Admin Panel,
Archived Chats, Workspace, Notes, Automations, Playground, Sign Out)
collapses the sidebar on mobile after navigating, but the Calendar entry
was missing this handling, leaving the sidebar open over the Calendar
page on mobile. Add the same mobile guard used by the sibling entries.
On latest `dev`, each sidebar section header in `Sidebar/Section.svelte` is a real `<button>` carrying `aria-expanded` and `aria-controls`, but it has **no activation handler**. The toggle comes only from `on:pointerup` on the wrapper inside `common/Collapsible.svelte`.
Keyboard activation dispatches a synthetic `click`, never `pointerup`, and that wrapper's own `on:click` handler calls `stopPropagation()`. So pressing Enter or Space on the header does nothing at all, while `aria-expanded` tells assistive technology this is a working disclosure control.
This affects every section in the sidebar: Models, Notes, Channels, Folders and Chats. Section state is persisted to `localStorage`, so a user whose section was collapsed on a previous visit has no keyboard way to open it again, and the content stays unreachable.
Breaks WCAG 2.1.1 Keyboard (Level A), and 4.1.2 Name, Role, Value (Level A), because the exposed expanded state belongs to a control that cannot be operated.
Fix: handle activation on the header button itself, where focus actually lands, and stop the now duplicate pointer path so a mouse click does not toggle twice. The existing inline `onChange` body is extracted to `setOpen` so the `change` dispatch and the `localStorage` write stay in one place and fire exactly once per toggle in both input modes. The adjacent "+" (`onAdd`) button already stops both `pointerup` and `click`, so it still does not toggle the section.
`Collapsible`'s wrapper cannot simply become a `<button>` instead, because its slot receives buttons from this component and others, so the fix belongs here.
`common/Folder.svelte` and `Sidebar/RecursiveFolder.svelte` have the same latent defect and are not touched by this PR.
Severity: Critical. Sidebar navigation cannot be expanded without a mouse.
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The sidebar time-ago indicator rendered `created_at`, so the relative time stayed pinned to the chat's creation age and never reflected new activity. After sending a message the chat would jump to the top of the list (which sorts by `updated_at`) while still showing a stale label such as "3w", which is confusing.
The indicator was originally added using `updated_at` and was inadvertently switched to `created_at` during a later refactor. Restore `updated_at` (falling back to `created_at` when absent) so the timestamp matches the list ordering and updates whenever a chat is modified.
Fixes#26451
Timothy Jaeryang Baek