feat: add new cards

[ThibaudDauce]

Extracted from #847

• Created ObjectCard base component with badges, media and default slots to provide a consistent card layout (border, hover, flex structure, fr-enlarge-link) shared across all horizontal cards. Created sub-components ObjectCardBadge (single badge only, uses absolute positioning), ObjectCardHeader and ObjectCardShortDescription (CSS line-clamp-2 + JS truncation to limit DOM size).
• Created new card components: TopicCard, PostCard, DiscussionMessageCard, and ReuseHorizontalCard (extracted from the horizontal/search mode of ReuseCard into its own component).
• Refactored DatasetCard and DataserviceCard to use ObjectCard. Added organization logo / avatar / placeholder on the left side of DataserviceCard, matching the layout of DatasetCard.
• Added consistent iconography across all cards using Remix Icons (RiDatabase2Line for datasets, RiTerminalLine for dataservices, RiLineChartLine for reuses, RiChat3Line for discussions, RiArticleLine for posts, RiBookShelfLine for topics), with aria-hidden="true" on all decorative icons.
• Extended Placeholder component with Dataservice and Topic types (RiTerminalLine and RiBookShelfLine).
• Fixed badge layout on DataserviceCard: removed conditional mt-2 that caused misalignment in grids when a card had badges next to one without.
• Fixed DiscussionCard (components/Discussions/) to guard against null closed_by with v-else-if.
• Used RiSubtractLine as separator consistently across all cards (replaced middle dots in TopicCard and DiscussionMessageCard).
• Added removeMarkdown to TopicCard description truncation, consistent with other cards.
• Updated the /design/cards page to showcase all card types in a 2-column grid, fetching data directly via useAPI.
• Moved types to datagouv-components: Page, Post, Comment, Thread.
• Changed Discussion types to use UserReference/OrganizationReference instead of full User/Organization. Adapted getOwnerEmails in utils/owner.ts to fetch user by ID since UserReference doesn't carry email.

Fix #867

[nicolaskempf57]

I have an overflow issue on the topic card only

[ThibaudDauce]

Fixed in 633ac99 (I've created a new component to have the same logic everywhere)

[nicolaskempf57]

I think it fixes #867 too