Replace ~150 hardcoded Tailwind color classes (bg-zinc-*, text-zinc-*,
border-white/*, text-cyan-*, bg-cyan-*) with CSS custom properties
(--pc-*) across all 17 components.
Add @theme block in index.css for Tailwind v4 theme-aware utility
classes (bg-pc-elevated, text-pc-text, border-pc-border, etc.).
Add --pc-hover, --pc-hover-strong, --pc-separator variables per theme
(white/alpha for dark/OLED, black/alpha for light).
Theme switcher (dark/light/OLED) now actually works — all UI elements
respond to theme changes in real-time.
Fixes#55
Shows how long the agent has been thinking (e.g. '5s', '1m 23s').
Timer appears after 2 seconds to avoid flicker on fast responses.
Helps users gauge if a request is still processing or stuck.