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>

nextcloud_mcp_server/api/__init__.py

@@ -0,0 +1,6 @@
+"""Management API for Nextcloud MCP Server.
+
+Provides REST endpoints for the Nextcloud PHP app to query server status,
+user sessions, and vector sync metrics. All endpoints use OAuth bearer token
+authentication via the UnifiedTokenVerifier.
+"""