feat(sharing): add document sharing with expiring links

- Add SharedLink model with token, expiry, view limit, password hash
- Add migration 025_add_shared_links
- Add API endpoints: create, list, revoke (auth) + public info/download
- Add management UI at /shared-links with revoke controls
- Add public share landing page at /share/{token}
- Add Share button on file_view.html
- Add Shared Links to user dropdown in common.js
- Write 35 unit tests covering all scenarios
- Update UserGuide.md with sharing documentation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/views/shared_links.py

@@ -0,0 +1,24 @@
+"""View route for the Shared Links management page.
+
+Renders the ``shared_links.html`` template where authenticated users can
+create, view, and revoke their document share links.
+"""
+
+import logging
+
+from fastapi import APIRouter, Request
+
+from app.views.base import require_login, templates
+
+logger = logging.getLogger(__name__)
+router = APIRouter()
+
+
+@router.get("/shared-links")
+@require_login
+async def shared_links_page(request: Request):
+    """Render the Shared Links management page."""
+    return templates.TemplateResponse(
+        "shared_links.html",
+        {"request": request, "page_title": "Shared Links"},
+    )