[gui] Show stations on Origins tab map when F9 is toggled

[comoglu]

Summary

• Extends EventEdit to display arrival stations on the Origins tab map, mirroring the existing station display already implemented on the Focal Mechanism tab
• Stations appear when the F9 Show Stations action is toggled, colored by arrival time residual using the scheme colors
• Lines are drawn from the selected origin dot to each station
• Generalizes StationLayer constructor to QWidget* and refSymbol to Map::Symbol* so the layer is reusable outside FMMap

Changes

• StationLayer: constructor FMMap* → QWidget*, refSymbol type ExtTensorSymbol* → Map::Symbol*
• EventEdit::init(): add StationLayer and AnnotationLayer to _originMap, both hidden by default
• EventEdit::updateOriginStations(): populate stations from arrivals — picks resolved via Pick::Find() with DatabaseQuery fallback (owned by PickPtr), station locations from inventory, distance/azimuth fallback when no pick is available
• EventEdit::drawStations() / drawStationAnnotations(): extended to also toggle the Origins tab layers
• EventEdit::currentOriginChanged(): calls updateOriginStations() on selection change
• EventEdit::resetOrigin(): clears station layer and annotations

Test plan

• Open scolv and select an event on the Event tab
• Switch to the Origins tab
• Select different origins in the list
• Toggle F9 (Show Stations) — stations should appear/disappear colored by time residual with connector lines to the origin
• Verify behavior matches the Focal Mechanism tab station display
• Verify F9 state is preserved when switching between origins