Seed historical net worth snapshots and trigger live price sync on demo startup

- seed.py: adds 30 weekly NetWorthSnapshot rows (Sep 2025 → Apr 2026) so the
  Net Worth chart has full history on first boot, not just today's value
- main.py: fires price_sync_job and fx_sync_job in the background immediately
  after the scheduler starts in demo mode, so portfolio valuations are live
  from the moment the container becomes healthy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/demo/seed.py

@@ -12,7 +12,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.core.security import encrypt_field, hash_password
 from app.db.models import (
     Account, Asset, Budget, Category, InvestmentHolding,
-    InvestmentTransaction, ManualCGTDisposal, Payslip,
+    InvestmentTransaction, ManualCGTDisposal, NetWorthSnapshot, Payslip,
     TaxProfile, Transaction, User,
 )
 
@@ -501,3 +501,56 @@ async def seed_demo(db: AsyncSession) -> None:
     ))
 
     await db.flush()
+
+    # ── Historical net worth snapshots (weekly, Oct 2025 → present) ───────
+    # Plausible progression: cash + growing investment portfolio, salary in
+    # each month, large purchases (car insurance Oct, Christmas Dec, etc.)
+    nw_history = [
+        # (date, total_assets, total_liabilities)
+        (date(2025,  9, 28),  "8150.00",    "0.00"),
+        (date(2025, 10,  5),  "8320.00",  "220.00"),   # VWRP+AAPL bought, Amex started
+        (date(2025, 10, 12),  "8050.00",  "680.00"),   # car insurance £485 hit
+        (date(2025, 10, 19),  "8750.00",  "820.00"),   # salary in, investments ticked up
+        (date(2025, 10, 26),  "9150.00",  "820.00"),
+        (date(2025, 11,  2),  "9820.00",  "820.00"),   # salary + BTC purchase Nov 1
+        (date(2025, 11,  9),  "9600.00",  "820.00"),   # slight market dip
+        (date(2025, 11, 16),  "9900.00",  "820.00"),
+        (date(2025, 11, 23), "10150.00",  "820.00"),
+        (date(2025, 11, 30), "10380.00",  "820.00"),
+        (date(2025, 12,  7), "10620.00",  "820.00"),
+        (date(2025, 12, 14), "10250.00", "1250.00"),   # Christmas spending on Amex
+        (date(2025, 12, 21), "10100.00", "1350.00"),   # VWRP 2nd buy + holiday spend
+        (date(2025, 12, 28), "10350.00", "1350.00"),   # post-Xmas, markets recovering
+        (date(2026,  1,  4), "10950.00", "1100.00"),   # new year, paid some Amex, markets up
+        (date(2026,  1, 11), "11350.00", "1100.00"),
+        (date(2026,  1, 18), "11700.00", "1100.00"),
+        (date(2026,  1, 25), "11500.00", "1100.00"),   # small dip
+        (date(2026,  2,  1), "12050.00", "1100.00"),   # salary in
+        (date(2026,  2,  8), "12450.00", "1100.00"),
+        (date(2026,  2, 15), "13050.00", "1100.00"),   # VWRP 3rd buy + market run
+        (date(2026,  2, 22), "13500.00", "1100.00"),
+        (date(2026,  3,  1), "14050.00", "1100.00"),   # salary in
+        (date(2026,  3,  8), "14450.00", "1100.00"),
+        (date(2026,  3, 15), "15000.00", "1050.00"),
+        (date(2026,  3, 22), "15500.00", "1042.50"),
+        (date(2026,  3, 29), "15650.00", "1042.50"),
+        (date(2026,  4,  5), "15680.00", "1042.50"),
+        (date(2026,  4, 12), "15710.00", "1042.50"),
+        (date(2026,  4, 19), "15740.00", "1042.50"),
+    ]
+    for snap_date, assets_str, liabs_str in nw_history:
+        assets = Decimal(assets_str)
+        liabs  = Decimal(liabs_str)
+        db.add(NetWorthSnapshot(
+            id=uuid.uuid4(),
+            user_id=uid,
+            date=snap_date,
+            total_assets=assets,
+            total_liabilities=liabs,
+            net_worth=assets - liabs,
+            base_currency="GBP",
+            breakdown={},
+            created_at=now,
+        ))
+
+    await db.flush()

backend/app/main.py

@@ -51,6 +51,15 @@ async def lifespan(app: FastAPI):
     from app.workers.scheduler import start_scheduler, stop_scheduler
     await start_scheduler()
 
+    # Demo: sync live prices and FX rates immediately so portfolio values are fresh
+    if settings.is_demo:
+        import asyncio
+        from app.workers.price_sync import price_sync_job
+        from app.workers.fx_sync import fx_sync_job
+        asyncio.ensure_future(price_sync_job())
+        asyncio.ensure_future(fx_sync_job())
+        logger.info("demo_background_sync_queued")
+
     logger.info("startup_complete", env=settings.environment)
     yield