feat: crypto portfolio analytics (history chart, allocation, P&L, cost basis)

Adds the analytics half of the CoinMarketCap reference: a value-over-time
chart (GET /crypto/history, forward-filled from AssetValuation like Net
Worth's own series but scoped to crypto assets), an allocation breakdown by
coin, and stat tiles for all-time profit, total invested (cost basis), and
best/worst performer.

Deliberately no "24h" range — history is only as dense as the sync cadence
(button or once/day), so a 24h chart would be one or two points, not a
smooth intraday line. Cost basis / all-time profit / best-worst performer
aren't separate endpoints: they're trivial to derive client-side from
fields already in GET /crypto/holdings, so no redundant backend logic.

Allocation card follows the dataviz skill's categorical rule: top 7 coins
by value get a fixed-order color from the app's already-validated 8-slot
ramp, an 8th+ folds into "Other" rather than generating a new hue.

82/82 backend tests passing (3 new for /crypto/history). Verified live
against the real CoinGecko API — and caught a real holding the user had
already added directly through the UI between messages, which the smoke
test correctly left untouched while cleaning up only its own test data.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01855PiW5Wd8n4aRW4n9kByY

backend/app/api/routes/crypto.py

@@ -3,6 +3,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.deps import get_session
 from app.schemas.crypto import (
+    CryptoHistoryResponse,
     CryptoHoldingCreate,
     CryptoHoldingRead,
     CryptoSearchResult,
@@ -11,9 +12,11 @@ from app.schemas.crypto import (
     CryptoTransactionRead,
 )
 from app.services.crypto_service import (
+    CRYPTO_RANGE_DAYS,
     add_transaction,
     create_holding,
     delete_transaction,
+    get_crypto_history,
     list_transactions,
     refresh_prices,
     search_coins,
@@ -68,3 +71,15 @@ async def delete_transaction_route(transaction_id: int, session: AsyncSession =
 @router.get("/search", response_model=list[CryptoSearchResult])
 async def search_coins_route(q: str = Query(min_length=1, max_length=100)) -> list[CryptoSearchResult]:
     return await search_coins(q)
+
+
+_HISTORY_RANGES = sorted(set(CRYPTO_RANGE_DAYS) | {"all"})
+_HISTORY_RANGE_PATTERN = f"^({'|'.join(_HISTORY_RANGES)})$"
+
+
+@router.get("/history", response_model=CryptoHistoryResponse)
+async def read_crypto_history(
+    range: str = Query(default="30d", pattern=_HISTORY_RANGE_PATTERN),
+    session: AsyncSession = Depends(get_session),
+) -> CryptoHistoryResponse:
+    return await get_crypto_history(session, range)