feat(auth): add admin user management dashboard

- Add UserProfile model (app/models.py) with per-user settings: display_name, daily_upload_limit, notes, is_blocked
- Add Alembic migration 013_add_user_profiles for the new table
- Add REST API at /api/admin/users/ with list, get, upsert (PUT), delete endpoints (admin-only)
- Add HTML template admin_users.html with Alpine.js: filterable user list, paginated table, edit/create modal, delete confirmation modal
- Add view handler at /admin/users (admin-only redirect guard)
- Register routers in app/api/__init__.py and app/views/__init__.py
- Add 'Users' link to admin nav dropdown in base.html (desktop + mobile)
- Add 27 tests covering auth, list, get, upsert, delete, and model constraints
- Register UserProfile in conftest.py model imports
- Document new endpoints in docs/API.md

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

migrations/versions/013_add_user_profiles.py

@@ -0,0 +1,42 @@
+"""Add user_profiles table for per-user admin settings
+
+Revision ID: 013_add_user_profiles
+Revises: 012_add_multi_user_support
+Create Date: 2026-03-06
+
+"""
+
+from typing import Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "013_add_user_profiles"
+down_revision: Union[str, None] = "012_add_multi_user_support"
+depends_on: Union[str, None] = None
+
+
+def upgrade() -> None:
+    """Create the user_profiles table."""
+    op.create_table(
+        "user_profiles",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("user_id", sa.String(255), nullable=False),
+        sa.Column("display_name", sa.String(255), nullable=True),
+        sa.Column("daily_upload_limit", sa.Integer(), nullable=True),
+        sa.Column("notes", sa.Text(), nullable=True),
+        sa.Column("is_blocked", sa.Boolean(), nullable=False, server_default=sa.text("0")),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.text("CURRENT_TIMESTAMP")),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.text("CURRENT_TIMESTAMP")),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_user_profiles_id", "user_profiles", ["id"])
+    op.create_index("ix_user_profiles_user_id", "user_profiles", ["user_id"], unique=True)
+
+
+def downgrade() -> None:
+    """Drop the user_profiles table."""
+    op.drop_index("ix_user_profiles_user_id", table_name="user_profiles")
+    op.drop_index("ix_user_profiles_id", table_name="user_profiles")
+    op.drop_table("user_profiles")