Add Coach, take the reference's colours and copy its nav and motion

Coach is the centre tab: questions about routines, slips, streak, today,
active time and debt, answered on the device from the user's own data,
with a target bar chart and buttons that start routines or open the right
screen. The palette moves to neutral grey, near-black and one orange
accent, and Home's header becomes a light panel. The nav is now
overlapping frosted circles whose active disc pops forward, and tabs fade
and rise in on switch. Goals leaves the nav for Coach and stays one tap
away in Home's category row.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KhQh614DMeYoQEH9SoMRUw

frontend/CLAUDE.md

@@ -109,7 +109,7 @@ status field. That's what makes honest history and excuse analysis possible.
 
 ## 6. Design language
 
-See `design.md`. In short: sage-to-cream ambient backdrop, frosted glass
+See `design.md`. In short: neutral light-grey backdrop with one orange accent, frosted glass
 controls, painted `SceneArt` instead of photos, image-led cards, two-tone
 greetings, night buttons with a lime spark, softly rounded corners (never
 pill-soft) and a floating round-button nav that switches tabs in place.