fix(newsfeed): tighten card spacing and reposition pinned icon (#818)

* fix(newsfeed): tighten card spacing and reposition pinned icon

- Move pinned icon to top-left corner with a tilted rotation
- Remove the extra pin row that added excess top padding
- Reduce spacing between post content, reactions, and comments
- Remove card box shadow

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(newsfeed): place pinned icon on card corner instead of avatar

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(newsfeed): stop dropdown menus locking body scroll

bits-ui defaults DropdownMenu.Content's preventScroll to true, so every
open ran a body scroll lock: a forced full-document style recalc and
reflow, a horizontal shift by the scrollbar width, and pointer-events:
none on the body. On the newsfeed page — a long list of cards each with
a scrollable comment thread — that made the comment ellipsis menu feel
sluggish to open. Menus don't need scroll locking; only modal layers do.

Also tighten card spacing, use the primary color for the pinned icon,
give the card menu trigger a pointer cursor, and switch the comment
save and submit buttons to the loading and secondary variants.

* refactor(newsfeed): store reply targets as data, not markup

Replies used to prepend a presentational <blockquote> — Tailwind classes,
hardcoded English and a copied snippet of the parent — onto the comment
body, and that whole string was persisted to course_newsfeed_comment.content.
Editing a reply therefore showed raw markup in the textarea, the quoted
snippet froze at write time, the label could never be localized, and two of
its ui: utilities never compiled because they appeared only in dashboard code.

Add a replyToCommentId column, distinct from parentId (the thread root), so
a reply can name the comment it answers. The service verifies the target
belongs to the same feed and the same thread; the paginated query joins it
to return replyToAuthorFullname, so the label is rendered from live data by
the new CommentTree.ReplyingTo component using the existing replying_to key.

Rows written the old way still display their stored quote, and
stripLegacyReplyQuote keeps that markup out of the edit textarea.

* refactor(newsfeed): drop redundant comments on reply target plumbing

* fix(newsfeed): address review feedback on pinned icon and quote stripping

- The pin icon carried an unprefixed `text-muted-foreground` plus
  `ui:stroke-primary`, which is emitted nowhere because it appears only in
  dashboard code, so the outline fell back to the muted colour. Use
  `ui:text-primary` and let the stroke inherit currentColor.
- Give the pinned state an accessible name: the icon is `aria-hidden`, and
  header.svelte no longer carries an indicator, so screen readers had nothing.
- Filter feeds on `isPinned` alone. `is_pinned` is only the database column
  name; drizzle maps it to `isPinned` and the API never returns the snake_case
  form, so the `as any` fallback was dead and let the page and card disagree.
- `ui:transition-color` is not a Tailwind utility and emitted nothing; the
  plural `ui:transition-colors` is what applies the transition.
- Strip a legacy reply quote only when the blockquote carries the `reply-quote`
  class the old code always wrote, so a blockquote the author typed is kept.

* docs(agents): forbid presentational markup in persisted content columns

---------

AGENTS.md

@@ -58,6 +58,27 @@ Also run `pnpm format:check` (see Translation, Formatting, and Git Workflow abov
   org.limits = { students: toResourceUsage(studentsUsed, studentsLimit) };
   ```
 
+## Persisted columns store data, not presentation
+
+A user-content column (`content`, `body`, `description`, …) stores what the author typed and nothing else. Check this **at the write site** — the component or service building the value — not at the schema.
+
+Never write into such a column:
+
+- **Presentational markup** — wrapper elements, Tailwind classes, inline styles. Render that in a component instead.
+- **Localized strings** — copy baked in at write time can never be re-translated, and it freezes the author's locale for every future reader.
+- **Copied values from another row** — a quoted snippet, an author name, a title. Store the relationship (a real FK column) and join or derive the display value at render time, so it stays correct when the source row is edited or deleted.
+
+```ts
+// ❌ don't — markup, English copy and a copy of the parent all land in the column
+const quote = `<blockquote class="...">Replying to @${target.fullname}"${target.snippet}"</blockquote>`;
+await createComment(`${quote}${text}`, parentId);
+
+// ✅ do — persist the relationship, render the label from live data
+await createComment(text, parentId, target.commentId);
+```
+
+The tell that this went wrong: an edit form shows raw markup, because the markup *is* the content.
+
 ## Creating a New Route
 
 ### Step 1: Validation Schema