Grey nodes not heard on the current LoRa config #387

Implement the unheard-since-config-change marker per the design spec: meshtastic/design#146. Needs meshtastic/firmware#11745 via a protobufs pin bump.

Consumes NodeInfo.heard_on_current_lora - derives nothing, so no timestamp, no persisted UI state, no db.uiConfig field, and none of the clock problems.

• Plumb it: ViewController forwards only num/channel/last_heard/user out of NodeInfo, so add it to both addOrUpdateNode overloads and to addNode/updateNode.
• Store it: the LVGL tree is the model - per-field values live in child user_data slots. Packing the bit alongside channel on the panel beats a twelfth slot.
• Render it: in applyNodesFilter, which already runs per row and ends with a reset-to-default. Use Themes::recolorText rather than a hand-rolled colour. Keep it distinguishable from the offline treatment.
• Refresh: updateLastHeard only calls applyNodesFilter on an offline→online transition, so a node re-heard while already online keeps its grey until the next sweep. Widen it.

TFTView_320x240 is the only view with a node list. Build on master, not on #381 - that PR rewrites all of this and is currently conflicting.

See design#146 for states and copy.