feat: redesign KPI overview — card grid with full value display + daily growth %

refactor: replace pie chart with horizontal bar chart for cost by provider

feat: replace provider chips with donut pie chart + legend

fix: revert chart Y-axis to cost USD, remove token axis

fix: chart tooltip — frosted glass background, centered above cursor

fix: restore hover tooltip on chart dots showing cost only

feat: change cost chart Y-axis to token count (M/K units), show cost labels on dots

refactor: replace chart preset buttons with compact dropdown select

feat: replace bar chart with SVG line chart + range filter for cost over time

feat: add pagination + live search to admin users table

fix: truncate pagination to avoid overflow with many pages

refactor: apply my_submissions UI style to admin submissions table

feat(auth+db): session-aware nav, ownership fix, admin hardening, schema cleanup