feat(astrolabe): add 3D PCA visualization for semantic search

- Add Plotly.js 3D scatter plot showing search results in PCA space
- Create shared visualization.py module to avoid code duplication
- Pass include_pca parameter through API chain to enable coordinates
- Fix OAuth redirects to use /settings/user/astroglobe

The visualization shows document embeddings projected to 3D via PCA,
with the query point highlighted in red. Uses Viridis colorscale
for score visualization, matching the existing vector-viz page.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

third_party/astroglobe/package.json

@@ -22,6 +22,7 @@
     "@nextcloud/l10n": "^3.1.0",
     "@nextcloud/router": "^3.0.1",
     "@nextcloud/vue": "^8.29.2",
+    "plotly.js-dist-min": "^2.35.3",
     "vue": "^2.7.16",
     "vue-material-design-icons": "^5.3.1"
   },