Rework balances around per-parent days left and deduce the partner from FK

Manual entry now takes one parent's sjukpenningnivå, lägstanivå and
dubbeldagar left (plus optional reserved days) and derives the rest in
build_snapshot, shared with the scraper. The scraper also reads the
family panel and exposes a partner deduction; with two parents it is
saved as a 'deduced' snapshot (migration 002). Parent count is the single
source of entitlement: one member gets 480 days and 96 savable at age 4,
two get 240 and 48 each. Workspaces are capped at two parents.

Also lands the in-flight squash of migrations 002–011 into the initial
schema and the removal of planning_mode.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/scripts/demo_plan.py

@@ -124,8 +124,7 @@ def _build_input() -> tuple[AllocationInput, dict]:
     alloc_input = AllocationInput(
         today=TODAY,
         horizon_end=horizon_end,
-        planning_mode="couple",
-        age4_savable_cap=resolve_age4_savable_cap("couple", parent_count=2),
+        age4_savable_cap=resolve_age4_savable_cap(parent_count=2),
         children=[child],
         parents=[parent_1, parent_2],
         pools=pools,

backend/scripts/seed_demo.py

@@ -214,7 +214,6 @@ async def _seed(conn: aiosqlite.Connection, *, reset: bool) -> None:
         email=DEMO_EMAIL, password=DEMO_PASSWORD, display_name=DEMO_NAME
     )
     workspace_id = alex.workspace_id
-    await services.workspace.update_workspace(workspace_id, planning_mode="couple")
 
     # -- 2. Partner (no login — shared/partner planning needs a second parent
     # on the workspace, but nothing requires them to have registered) -------
@@ -261,15 +260,10 @@ async def _seed(conn: aiosqlite.Connection, *, reset: bool) -> None:
         workspace_id=workspace_id,
         child_id=child.id,
         total_days=240,
-        days_used=240,
-        reserved_days_total=90,
+        sjukpenning_left=0,
+        lagsta_niva_left=0,
         reserved_days_left=0,
-        transferable_days_left=0,
         dubbeldagar_left=55,
-        sjukpenning_total=195,
-        sjukpenning_used=195,
-        lagsta_niva_total=45,
-        lagsta_niva_used=45,
     )
 
     # -- 6. Day overrides -----------------------------------------------
@@ -398,7 +392,7 @@ def _print_summary(
     print(f"  Password: {DEMO_PASSWORD}")
     print()
     print("Created:")
-    print(f"  Workspace id: {workspace_id} (planning_mode=couple)")
+    print(f"  Workspace id: {workspace_id} (couple: 2 parents)")
     print(f"  Parent 1:     {DEMO_NAME} ({alex.uuid}) — has a login, near-drained FP pool")
     print(f"  Parent 2:     {PARTNER_NAME} ({sam.uuid}) — no login, large surplus pool")
     print(f"  Child:        {CHILD_NAME} ({child_id}), born {birth_date.isoformat()}")