Integrate Build Canada design system

[xrendan]

Summary

• Add Build Canada color palette (linen, auburn, cerulean, charcoal, gray scales)
• Update typography to use Geist Sans and Inter font stacks
• Restyle buttons, tabs, timeline, dropdowns, and controls with new design tokens
• Remove border-radius from popups, tooltips, modals, and settings menus
• Simplify ActionButtons to use CSS-only layout (removes JS width calculations)
• Simplify NoDataModal to plain text on linen background
• Update Footer to use fixed estimates instead of computing ActionButtons width

Test plan

• Verify chart components render correctly in Storybook
• Check buttons, tabs, and controls have correct styling
• Confirm popups/tooltips have no border-radius
• Test action buttons (Download, Share, Donate, Explore) display correctly
• Verify empty state shows plain text on linen background

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