refactor(astrolabe): replace client-side PDF.js with server-side PyMuPDF rendering

Replace the client-side PDF.js viewer with server-side rendering using PyMuPDF.
This avoids CSP worker restrictions and ES private field access issues that
affected Chromium browsers.

Changes:
- Add /api/v1/pdf-preview endpoint to MCP server (management.py)
- Add pdf-preview route and controller action in Astrolabe PHP backend
- Refactor PDFViewer.vue to display server-rendered PNG images
- Remove pdfjs-dist dependency and client-side PDF loading code
- Use @nextcloud/axios for CSRF token handling in PDFViewer

The server downloads the PDF via WebDAV, renders the requested page with
PyMuPDF at the specified scale, and returns a base64-encoded PNG image.

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

nextcloud_mcp_server/app.py

@@ -2119,6 +2119,7 @@ def get_app(transport: str = "streamable-http", enabled_apps: list[str] | None =
             get_app_password_status,
             get_chunk_context,
             get_installed_apps,
+            get_pdf_preview,
             get_server_status,
             get_user_session,
             get_vector_sync_status,
@@ -2179,6 +2180,8 @@ def get_app(transport: str = "streamable-http", enabled_apps: list[str] | None =
         routes.append(
             Route("/api/v1/chunk-context", get_chunk_context, methods=["GET"])
         )
+        # PDF preview endpoint for Astrolabe (server-side rendering)
+        routes.append(Route("/api/v1/pdf-preview", get_pdf_preview, methods=["GET"]))
         # ADR-018: Unified search endpoint for Nextcloud PHP app integration
         routes.append(Route("/api/v1/search", unified_search, methods=["POST"]))
         routes.append(Route("/api/v1/apps", get_installed_apps, methods=["GET"]))
@@ -2193,7 +2196,7 @@ def get_app(transport: str = "streamable-http", enabled_apps: list[str] | None =
             "/api/v1/users/{user_id}/session, /api/v1/users/{user_id}/revoke, "
             "/api/v1/users/{user_id}/app-password, "
             "/api/v1/vector-viz/search, /api/v1/search, /api/v1/apps, "
-            "/api/v1/webhooks"
+            "/api/v1/webhooks, /api/v1/pdf-preview"
         )
 
     # ADR-016: Add Smithery well-known config endpoint for container runtime discovery