feat: user path to resume BT from low-memory pause via reader menu toggle

Field session: after a recovery teardown the heap settles at ~72 KB --
below the 100 KB start floor -- and never recovers on its own (the
defrag silent-restart only fires when a build FAILS, and builds succeed
now). BT stayed paused forever, the menu toggle claimed ON, and toggling
off/on changed nothing.

- Menu label tells the truth: ON / PAUSED (enabled but stack down) / OFF
  (new STR_STATE_PAUSED string)
- Toggling BT on below the heap floor silent-restarts into the current
  book: the fresh boot's ~118 KB passes the gate and BT auto-starts on
  resume. Explicit user intent is the right trigger for the defrag.
- Hoist the floor to bleinput::kStartMinFreeHeap, shared by the
  lifecycle gate and the toggle

lib/I18n/translations/english.yaml

@@ -299,6 +299,8 @@ STR_BT_NO_PAIRED: "No paired devices"
 STR_BT_MAP_BUTTONS: "Map Remote Buttons"
 STR_BT_PRESS_REMOTE: "Press a button on your remote"
 STR_BT_CONNECTING_POPUP: "BT Connecting..."
+STR_BT_PAUSED_LOW_MEM_POPUP: "BT paused (low memory)"
+STR_STATE_PAUSED: "PAUSED"
 STR_BT_PAGE_FORWARD: "Page Forward"
 STR_BT_PAGE_BACK: "Page Back"
 STR_BT_FORGET_PROMPT: "Hold Confirm to forget"