Add dark mode palettes + Woodpecker CI pipeline

- Add 2 dark palettes (Nuit, Ocean) to DisplaySettings with full SVG
  theme tokens — all hardcoded SVG colors (grids, legends, text fills,
  pills, dot strokes, drag handles) replaced with reactive bindings
- Update scoped CSS to use var(--color-*) and var(--svg-*) throughout
- Add Woodpecker CI pipeline (.woodpecker.yml): build → docker push → deploy
- Add multi-stage Dockerfiles for backend (Python) and frontend (Nuxt)
- Add production docker-compose with Traefik labels + dev override
- Remove old single-stage Dockerfiles and root docker-compose.yml
- Update Makefile with docker-dev target
- Exclude data files (pdf, xls, ipynb) from git

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/app/pages/login/commune.vue

@@ -24,7 +24,7 @@
       </form>
 
       <!-- Dev credentials hint -->
-      <div v-if="isDev" style="margin-top: 1rem; padding: 0.75rem; background: #fef3c7; border: 1px solid #f59e0b; border-radius: 6px; font-size: 0.8rem;">
+      <div v-if="isDev" class="dev-hint">
         <strong>Dev:</strong> saou@sejeteralo.fr / saou2024
       </div>
     </div>