refactor(multiboards): remove time filter system end-to-end

Backend retention now keeps only recent posts, making the time filter UI
and newerThan filtering obsolete. Deleted use-time-filter hook, canonical
multiboard routes only, removed footer suggestions, dropped i18n keys.

public/translations/en/default.json

@@ -140,7 +140,6 @@
   "sort_by": "Sort by",
   "subplebbit_offline_info": "This board might be offline and publishing might fail",
   "posts_last_synced_info": "Posts last synced {{time}}, this board might be offline and publishing might fail.",
-  "newer_than": "newer than",
   "no_threads": "No threads",
   "hidden": "hidden",
   "save_options": "Save Options",
@@ -189,8 +188,6 @@
   "no_board_selected_warning": "Please select a board before posting.",
   "invalid_url_alert": "The provided link is not a valid URL.",
   "empty_comment_alert": "Cannot post empty comment.",
-  "more_threads_last_week": "{{count}} threads since {{currentTimeFilterName}} — [<1>Show More Threads from Last Week</1>]",
-  "more_threads_last_month": "{{count}} threads since {{currentTimeFilterName}} — [<1>Show More Threads from Last Month</1>]",
   "newer_threads_available": "Newer threads available — [<1>Refresh</1>]",
   "stored_locally": "Stored locally (in {{location}} data), not synced across devices",
   "choose_one": "Choose one:",
@@ -199,7 +196,6 @@
   "reset_changes": "Reset Changes",
   "crypto_address_yours": "Crypto address belongs to this account.",
   "delete_wallet": "Delete Wallet",
-  "last_bumped": "Last Bumped",
   "fit_expanded_images_to_screen": "Fit expanded images to screen",
   "fit_expanded_images_to_screen_tip": "Limit expanded images to both browser width and height",
   "choose_file": "Choose File",
@@ -230,7 +226,6 @@
   "filter_and_highlights_help": "Filters & Highlights Help",
   "filter_and_highlights": "Filters & Highlights",
   "boards_you_moderate": "boards you moderate",
-  "more_threads_last_year": "{{count}} threads since {{currentTimeFilterName}} — [<1>Show More Threads from Last Year</1>]",
   "moderator_of_this_board": "This user is a moderator of this board",
   "administrator_of_this_board": "This user is an administrator of this board",
   "copy_content_id": "Copy content ID",