Add refresh timer to web dashboard

[toodimes]

Context

Implements refresh countdown timer for Symphony web dashboard as requested in Linear ticket AIW-6.

TL;DR

Added countdown timer showing 'Refreshes in Xs' to web dashboard status area that counts down and resets with each refresh.

Summary

• Added countdown timer display to web dashboard showing seconds until next refresh
• Implemented LiveView state management for real-time countdown updates
• Styled refresh countdown badge with accent colors matching existing design system
• Timer counts down from 1s to 0s and resets automatically after each dashboard update

Alternatives

• Could have used client-side JavaScript timer instead of LiveView, but LiveView provides better consistency
• Could have added timer to terminal UI, but web dashboard was specifically requested per ticket description

Test Plan

• make all
• Start Symphony with --port 4001 and verify countdown timer displays and functions correctly
• Verify all 198 tests pass with no regressions
• Confirm timer integrates properly with existing refresh mechanism