feat: respect system dark mode in dashboard

[pilipilisbot]

Summary

• Add system-driven light/dark color tokens for the dashboard.
• Let Tailwind semantic colors resolve through CSS variables and prefers-color-scheme.
• Add dark-mode compatibility rules for existing direct white, slate, and status-color utility usage.
• Preserve prefers-color-scheme media queries in the packaged dashboard build.
• Rebuild packaged dashboard static assets.

Closes #146.

Tests

• npm test
• npm run build
• pytest -q
• Verified generated packaged CSS keeps light tokens outside media queries and dark tokens inside @media (prefers-color-scheme: dark).
• Playwright screenshots captured locally with --color-scheme=light and --color-scheme=dark against the Vite dev server.

Screenshots

Dark-mode screenshot capture succeeded locally at /tmp/gab-dashboard-dark.png, but I could not upload it to GitHub from this environment because gh-image requires a browser user_session cookie or GH_SESSION_TOKEN; only token-based gh auth is available here.

[ecarreras]

@pilipilisbot revisa els conflictes

[pilipilisbot]

Conflicts resolved by merging the updated main into the PR branch and regenerating the packaged dashboard assets.

Pushed commit: 9dd3a17 (Merge main into issue-146-dark-mode). The PR diff is back to the intended dark-mode scope: dashboard CSS/Tailwind plus regenerated static asset hashes.

Local verification passed:

• npm test
• npm run build
• .venv/bin/python -m pytest -q (306 passed, 1 Starlette/httpx deprecation warning)

GitHub now shows the PR as merged; CI for the pushed head was still pending when I checked.

[pilipilisbot]

Follow-up on the merged PR: #147 is merged, and the refreshed GitHub Actions run for the merged head is green.

• dashboard: passed
• pytest (3.11): passed
• pytest (3.12): passed

No further code changes were needed after the conflict-resolution merge.