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/assets/css/main.css

@@ -15,6 +15,12 @@
   --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
   --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
   --chart-scale: 1;
+  /* SVG theme tokens (overridden by DisplaySettings palettes) */
+  --svg-plot-bg: #f8fafc;
+  --svg-grid: #e2e8f0;
+  --svg-legend-bg: white;
+  --svg-text: #334155;
+  --svg-text-light: #64748b;
 }
 
 * {
@@ -235,6 +241,61 @@ a:hover {
   to { transform: rotate(360deg); }
 }
 
+/* ── Dark mode overrides ── */
+.palette-dark body,
+.palette-dark {
+  color-scheme: dark;
+}
+
+.palette-dark .card {
+  background: var(--color-surface);
+  border-color: var(--color-border);
+}
+
+.palette-dark .btn-secondary {
+  background: var(--color-surface);
+  color: var(--color-text);
+  border-color: var(--color-border);
+}
+.palette-dark .btn-secondary:hover {
+  background: var(--color-bg);
+}
+
+.palette-dark .form-input {
+  background: var(--color-surface);
+  color: var(--color-text);
+  border-color: var(--color-border);
+}
+
+.palette-dark .alert-info { background: #1e3a5f; color: #93c5fd; border-color: #1e3a5f; }
+.palette-dark .alert-success { background: #14532d; color: #86efac; border-color: #14532d; }
+.palette-dark .alert-error { background: #450a0a; color: #fca5a5; border-color: #450a0a; }
+
+.palette-dark .badge-green { background: #14532d; color: #86efac; }
+.palette-dark .badge-blue { background: #1e3a5f; color: #93c5fd; }
+.palette-dark .badge-amber { background: #451a03; color: #fcd34d; }
+
+.palette-dark .table th,
+.palette-dark .table td {
+  border-bottom-color: var(--color-border);
+}
+.palette-dark .table th { color: var(--color-text-muted); }
+
+/* ── Dev hint ── */
+.dev-hint {
+  margin-top: 1rem;
+  padding: 0.75rem;
+  background: #fef3c7;
+  border: 1px solid #f59e0b;
+  border-radius: 6px;
+  font-size: 0.8rem;
+}
+.palette-dark .dev-hint {
+  background: #451a03;
+  border-color: #92400e;
+  color: #fcd34d;
+}
+
 /* ── Responsive table ── */
 @media (max-width: 480px) {
   .table th, .table td {