feat(post): post actions toolbar (share / copy / print / reading time)

Adds a small toolbar next to the comment-count badge with four actions:

- Share — uses `navigator.share()` on supporting devices, falls back
  to copy-link otherwise
- Copy link — clipboard API with `<input>` + `execCommand` fallback,
  flashes a checkmark for 1.5s on success
- Print — `window.print()`, hidden via `print:hidden` so it doesn't
  show up in the printed output itself
- Reading time — server-computed from headline+body HTML at ~200 wpm,
  hidden when 0

Reading time + canonical URL come from `+page.server.ts` so SSR
output is identical and shareable URLs render correctly.

All labels go through the translations layer (5 new
`post_action_*` keys).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/routes/post/[slug]/+page.svelte

@@ -7,6 +7,7 @@
   import Accordion from "$lib/components/Accordion.svelte";
   import CommentCountBadge from "$lib/components/CommentCountBadge.svelte";
   import Comments from "$lib/components/Comments.svelte";
+  import PostActions from "$lib/components/PostActions.svelte";
   import RustyImage from "$lib/components/RustyImage.svelte";
   import { t, T } from "$lib/translations";
   import type { PageData } from "./$types";
@@ -76,13 +77,18 @@
     </div>
   </div>
 </div>
-<div>
+<div class="flex flex-wrap items-center gap-x-4 gap-y-2 text-sm text-zinc-600">
   {#if data.commentPageId}
     <CommentCountBadge
       pageId={data.commentPageId}
       targetId="comments-section"
     />
   {/if}
+  <PostActions
+    url={data.canonicalUrl}
+    title={data.seoTitle}
+    readingTimeMinutes={data.readingTimeMinutes}
+  />
 </div>
 
 <article