Add semantic color tokens for light/dark modes

[AndreRobitaille]

Summary

• Implement a centralized semantic color token system (CSS variables) for light and dark modes.
• Replace hardcoded colors with tokens across existing CSS.
• Adjust light/dark palettes to reduce "too white" light mode and "too blue" dark mode.

Context

The current UI feels visually flat: light mode is overly white and dark mode is mostly shades of blue. We want calm civic authority with neutral bases and controlled accents.

Requirements

• Add a centralized color token file (CSS/SCSS) defining semantic variables (not component-specific colors).
• Define tokens for:
  • Background (page)
  • Surface (cards/rows/panels)
  • Surface subtle (alternate row background or hover)
  • Border / divider
  • Text primary / text secondary / text muted
  • Link / primary accent
  • Status colors (success, attention, danger, neutral)
• Implement both light and dark mode values using the same token names.
• Ensure contrast is acceptable for readability (especially text-muted vs background).

Design Intent

• Light mode:
  • Page background should be off-white (not pure white).
  • Cards/surfaces can be true white with subtle borders.
• Dark mode:
  • Page background and surfaces should be neutral charcoal/slate (not blue).
  • Blue becomes an accent, not the base background tone.

Non-requirements

• Do not change layout.
• Do not add new UI elements.
• Do not add fancy gradients.

Acceptance Criteria

• There is a single source of truth for theme colors.
• Existing CSS is updated to use tokens instead of hardcoded colors.
• Light mode and dark mode feel clearly distinct and less fatiguing.

Token Names (examples)

• --c-bg
• --c-surface
• --c-surface-2
• --c-border
• --c-text
• --c-text-2
• --c-text-3
• --c-link
• --c-success
• --c-attention
• --c-danger
• --c-neutral

[AndreRobitaille]

Closing as already satisfied. The codebase has a comprehensive CSS variable system (~50+ tokens) with semantic naming (--color-bg, --color-surface, --color-text, etc.), full light/dark mode support via data-theme attribute, warm neutral palettes (off-white light mode, charcoal dark mode), and only 1 minor hardcoded color remaining. All acceptance criteria from the original issue are met.