feat: harden auth and study workflows

- replace plaintext login and unlock requests with RSA-OAEP/AES-GCM encrypted payloads

- add login challenge replay protection, production RSA key validation, and auth tests

- wire compose to environment-driven dev/prod settings without committing local secrets

- update setup-config smoke scripts and Postman docs for encrypted login

- add visit schedule migrations/tests and update study/subject setup workflows

backend/alembic/versions/20260508_01_replace_global_visit_window.py

@@ -0,0 +1,43 @@
+"""replace global visit window with per-visit schedule
+
+Revision ID: 20260508_01
+Revises: 20260331_01
+Create Date: 2026-05-08 11:30:00.000000
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+
+revision: str = "20260508_01"
+down_revision: Union[str, None] = "20260331_01"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "studies",
+        sa.Column(
+            "visit_schedule",
+            postgresql.JSONB(astext_type=sa.Text()),
+            nullable=False,
+            server_default=sa.text("'[]'::jsonb"),
+        ),
+    )
+    op.drop_column("studies", "visit_window_end_offset")
+    op.drop_column("studies", "visit_window_start_offset")
+    op.drop_column("studies", "visit_total")
+    op.drop_column("studies", "visit_interval_days")
+
+
+def downgrade() -> None:
+    op.add_column("studies", sa.Column("visit_interval_days", sa.Integer(), nullable=True))
+    op.add_column("studies", sa.Column("visit_total", sa.Integer(), nullable=True))
+    op.add_column("studies", sa.Column("visit_window_start_offset", sa.Integer(), nullable=True))
+    op.add_column("studies", sa.Column("visit_window_end_offset", sa.Integer(), nullable=True))
+    op.drop_column("studies", "visit_schedule")