Analytics tabs share icons #58

Three pairs of tabs in the Analytics sub-header use the same glyph:

• Mesh and Traffic both use MeshIcon
• Scopes and Neighbour Graph both use GraphIcon
• Observer and Compare observers both use ObserverIcon (this pair predates feat(stats): add region-aware scope analytics #53)

At a glance the row looks like something failed to render. Traffic and Scopes arrived in #53, so it went from one duplicate pair to three and is now hard to miss.

Fix is three new glyphs in TAB_OPTIONS in src/features/stats/StatsSubHeader.tsx. Nothing else needs to change.

Note #55 and #57 add RF / Signal and Paths tabs that reuse ObserverIcon and GraphIcon again, so worth sorting before those land.