feat(filters): "Share view" link button in the sidebar

Add a share button next to Clear all that copies a link reproducing the current
filter view (filters, sort, scope) to the clipboard, with a confirmation toast.
This is the opt-in replacement for the old always-on URL mirroring. Trilingual.

frontend/src/i18n/locales/en/sidebar.json

@@ -26,6 +26,9 @@
   "clearDates": "clear dates",
   "reshuffle": "Reshuffle",
   "noMatchingTags": "No matching tags here",
+  "shareView": "Copy a link to this view",
+  "shareCopied": "View link copied to clipboard",
+  "shareFailed": "Couldn't copy the link",
   "widget": {
     "show": "Show",
     "sort": "Sort",