feat(library): Import and Refresh behind one menu button

The library's top bar had a button each for Import and Refresh. Pulling
the list down refreshes too, and is the quicker way on a phone, so both
now sit in a menu ("Library options"), leaving the bar to Search.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -54,6 +54,7 @@
   "studysetCountFiles": "{count, plural, =1{1 file} other{{count} files}}",
   "@studysetCountFiles": {"placeholders": {"count": {"type": "int"}}},
   "libraryRefresh": "Refresh",
+  "libraryOptions": "Library options",
   "libraryImport": "Import",
   "libraryImportAnkiHint": "Becomes a studyset of its own, from an .apkg or .colpkg file",
   "libraryImportArchive": "Halkyon archive",