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/lib/translations.ts

@@ -162,6 +162,12 @@ const TRANSLATION_KEYS = [
   "comments_pending_summary_other",
   "comments_count_aria",
   "comments_jump_to",
+  // Post actions toolbar (share / copy link / print / reading time).
+  "post_action_share",
+  "post_action_copy",
+  "post_action_copied",
+  "post_action_print",
+  "post_action_reading_time",
 ] as const;
 
 export type TranslationKey = (typeof TRANSLATION_KEYS)[number];