fix: Stack title overflows into cards for read-only board members

[Superjamp]

Bug description

For users with read-only access to a board (canManage = false) or on archived boards, the list/stack column header title wraps to multiple lines and visually overlaps the cards below it. Users with manage rights see the title correctly truncated with ….

Steps to reproduce

1. Share a board with a user as read-only (no manage rights)
2. Log in as that user and open the board
3. The board must have at least one list with a long title

Result: Title wraps to multiple lines and overlaps the cards.
Expected: Title is truncated to a single line with …

Root cause

In src/components/board/Stack.vue there are two <h3> branches:

• Manageable (v-else-if="!editing"): has class="stack__title" → gets white-space: nowrap; overflow: hidden; text-overflow: ellipsis → correct.
• Read-only / archived (v-if="!canManage || isArchived"): plain <h3> without the class → no overflow constraints → wraps freely.

Environment

• Affects all browsers (Chrome, Firefox, WebKit)
• Reproducible on Nextcloud Deck v1.17.1