Fix CI/deploy: realign lockfile and revert breaking Dependabot major bumps

[pedrobritx]

What & why

CI and the GitHub Pages deploy were failing. Both workflows die at the npm ci step with:

npm error Invalid: lock file's next@16.2.10 does not satisfy next@15.5.20
npm error Invalid: lock file's @next/swc-linux-x64-gnu@16.2.10 does not satisfy @next/swc-linux-x64-gnu@15.5.20

Root cause: three premature Dependabot major bumps landed together and broke the last-green build (Pages deploy #29274388099, the last success before the failures started). This PR realigns the tree with the versions the project is actually written for:

• next — lockfile only. package-lock.json carried next@16.2.10 while package.json still declares ^15.5.0, so npm ci's strict check rejected the tree. Regenerating the lockfile pins next back to 15.5.20 (within ^15.5.0). No package.json change needed here — the merge left the lockfile inconsistent.
• typescript ^7.0.2 → ^5.9.3. TS 7 broke next build: Next stopped resolving the tsconfig @/* path alias, producing spurious Module not found errors for @/components/* and @/lib/*; tsc --noEmit also errored on the global CSS side-effect imports. Reverting fixes both.
• tailwindcss ^4.3.2 → ^3.4.19. Tailwind v4 moved its PostCSS plugin to @tailwindcss/postcss and rejects being used directly. The project is written for v3 (@tailwind base/components/utilities, tailwind.config.ts, tailwindcss: {} in postcss.config), so v4 failed at CSS processing. Reverting keeps everything consistent with zero code changes.

Only package.json (two devDependencies) and package-lock.json change; no application code is touched.

Note: the next@16, typescript@7, and tailwindcss@4 upgrades are all real majors worth doing later — but each needs its own migration PR (Tailwind v4's CSS-first config, Next 16 codemods, TS 7 adjustments), not a silent Dependabot merge.

How to test

Runs green locally on Node 22; the CI matrix runs the same steps:

npm ci            # was failing here — now clean
npm run typecheck # 0 errors
npm run lint      # clean
npm test          # 12 files, 77 tests passed
npm run build     # static export of all 11 routes to ./out

Device class unaffected — this is a build/toolchain fix, no runtime/UI change.

Checklist

• npm run typecheck, npm run lint, npm test, and npm run build pass
• Accessibility considered: no UI change (dependency/build fix only)
• Only open-access (public domain / CC0) art is surfaced; credit is preserved (unchanged)
• Tests added or updated for behaviour changes (n/a — no behaviour change)
• Docs / CHANGELOG updated if relevant (n/a)

🤖 Generated with Claude Code

---

Generated by Claude Code