feat(ui): SolarPanel icon, dominant-source home color, FV label above (#68)

[gnacho]

Closes #68

Summary

Replaces the Sun icon with the lucide SolarPanel icon for PV production and gives the flow-diagram home node a lucide House icon whose color reflects the dominant incoming source.

• PV icon: SolarPanel, amber while producing (> 0.1 kW) and grey when idle (night/offline), in the "Now" band and the FV flow node.
• Home node: lucide House icon (replaces the hand-drawn SVG FlowHomeIcon, which was removed). Color follows the dominant incoming source: battery → green, grid → red, PV → amber, and neutral grey when there is no consumption.
• Flow diagram layout: FV label moved above the node so it no longer overlaps the outgoing flows; diagram shifted down and viewBox enlarged; PV cable lengthened by tightening the top/bottom margins.

Verification

• Build OK, lint 0 errors, theme-audit OK.
• Playwright geometric check on the dev server: FV text above node, home text below node, 0 text/path overlaps.
• Deployed to CT 226, md5 prod==local, HTTP+HTTPS 200.