Let a household choose to be paid for the red days

Asking for a full week off never spent anything on the Saturday, the
Sunday or a holiday, and a test now says so outright rather than leaving
it to be rediscovered. Those days are free because vacation cannot be
taken on a day that is not a working day.

Parental benefit is a payment rather than a schedule, though, so it can
be drawn on a red day to turn an unpaid day off into a paid one — at the
cost of a day the family would otherwise keep. That is now a workspace
setting, off by default, and it never reaches for a vacation day. With it
off the planner behaves exactly as before.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ei7gCZzdd751uZtPzb1Pep

backend/migrations/versions/003_add_take_pl_on_red_days.py

@@ -0,0 +1,38 @@
+"""Add workspace.take_pl_on_red_days.
+
+Per-workspace opt-in (default off) letting the planning engine fund a free
+day (Saturday, Sunday, public holiday) with a parental-benefit day instead of
+leaving it unpaid — never with a vacation day, since Swedish law does not let
+you "take vacation" on a day that already isn't a working day. See
+`app.services.allocation_service.REASON_FP_RED_DAY` and
+`AllocationInput.take_pl_on_red_days`.
+
+A plain `ADD COLUMN` suffices here (unlike 002's CHECK-constraint change,
+which needed a full table rebuild) since SQLite supports adding a NOT NULL
+column with a constant DEFAULT directly.
+
+Must stay byte-for-byte equivalent to the `workspace` table in
+`app/db/connection.py`'s `_FULL_SCHEMA` — `tests/integration/test_schema_parity.py`
+asserts exactly that.
+
+Revision ID: 003
+Revises: 002
+Create Date: 2026-09-19
+"""
+
+from __future__ import annotations
+
+from alembic import op
+
+revision: str = "003"
+down_revision: str | None = "002"
+branch_labels: str | None = None
+depends_on: str | None = None
+
+
+def upgrade() -> None:
+    op.execute("ALTER TABLE workspace ADD COLUMN take_pl_on_red_days BOOLEAN NOT NULL DEFAULT 0")
+
+
+def downgrade() -> None:
+    op.execute("ALTER TABLE workspace DROP COLUMN take_pl_on_red_days")