feat(api): add advanced filtering and saved searches

- Add date range (date_from/date_to), storage provider, and tags filters to GET /api/files
- Add SavedSearch model and migration (005_add_saved_searches)
- Add CRUD API endpoints for saved searches at /api/saved-searches
- Update files.html template with new filter controls and saved searches UI
- Update files view to pass new filter parameters to template
- Add comprehensive tests for all new functionality (26 tests)

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

migrations/versions/005_add_saved_searches.py

@@ -0,0 +1,36 @@
+"""Add saved_searches table for user-defined filter combinations
+
+Revision ID: 005_add_saved_searches
+Revises: 004_add_search_fields
+Create Date: 2026-03-01
+
+"""
+
+from typing import Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "005_add_saved_searches"
+down_revision: Union[str, None] = "004_add_search_fields"
+depends_on: Union[str, None] = None
+
+
+def upgrade() -> None:
+    """Create saved_searches table."""
+    op.create_table(
+        "saved_searches",
+        sa.Column("id", sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column("user_id", sa.String(), nullable=False, index=True),
+        sa.Column("name", sa.String(), nullable=False),
+        sa.Column("filters", sa.Text(), nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.UniqueConstraint("user_id", "name", name="unique_user_search_name"),
+    )
+
+
+def downgrade() -> None:
+    """Drop saved_searches table."""
+    op.drop_table("saved_searches")