feat: revamp line charts with premium visuals

[vide]

Summary

Visual overhaul of all line charts across the app (ChargeDetail, DriveDetail, CurrentCharge screens) to look premium and modern, inspired by Robinhood/Tesla/Home Assistant chart designs.

Visual enhancements

• Smooth cubic Bezier curves — monotone interpolation (Fritsch-Carlson method) replaces jagged lineTo() segments, with guaranteed no-overshoot
• Gradient fill under each line (color → transparent), with lower alpha for dual-axis charts to avoid occlusion
• Dashed vertical crosshair on point selection
• Subtle dashed grid lines — 3 interior lines at 15% opacity (was 5 solid lines at 30%)
• Glowing data point indicator — 3-layer glow replaces basic bullseye
• Animated line drawing — 800ms ease-out entrance animation on first appearance
• Theme-aware tooltips — inverseSurface/inverseOnSurface with shadow, replaces hardcoded dark gray
• Dual-axis tooltip — colored dot prefixes per series with time label

Code improvements

• Extracted shared utilities to ChartDrawUtils.kt (LTTB downsampling, monotone cubic path builder, grid/label/chip/crosshair/indicator drawing)
• Unified duplicated LTTB algorithm between single and dual-axis charts
• Removed unused Vico dependency (vico-compose-m3 beta)
• Fixed AAPT error in ic_launcher_accent.xml (?attr/colorPrimary → hardcoded color)

Unchanged

• Cross-chart synchronization via sharedXFraction
• Fullscreen landscape mode
• LTTB downsampling (150 point cap)
• Y-axis (4 labels) and X-axis (5 labels) layout
• All screen-level code (no API changes)

Test plan

• ChargeDetailScreen: verify smooth curves, gradient fill, crosshair, synced tooltips across all 5 charts
• DriveDetailScreen: verify power chart zero-line still renders correctly with gradient, all 4 charts sync
• CurrentChargeScreen: verify dual-axis (Voltage+Current) gradient fills don't occlude, colored dot tooltip
• Fullscreen: tap expand icon on any chart — landscape mode works, chart fills screen
• Scroll performance: no jank when scrolling through multiple charts
• Entrance animation: line draws in from left over ~800ms when navigating to detail screens

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