feat: add DeFi data via DefiLlama API (TDD)

7 new endpoints under /api/v1/defi/ (all free, no API key):
- GET /defi/tvl/protocols - top DeFi protocols by TVL
- GET /defi/tvl/chains - chain TVL rankings
- GET /defi/tvl/{protocol} - single protocol TVL
- GET /defi/yields - top yield pools (filter by chain/project)
- GET /defi/stablecoins - stablecoin market data
- GET /defi/volumes/dexs - DEX volume overview
- GET /defi/fees - protocol fees/revenue overview

Data source: DefiLlama API (free, no key needed)
58 new tests (33 service + 25 route). All 561 tests passing.

routes_defi.py

@@ -0,0 +1,75 @@
+"""DeFi data routes via DefiLlama API."""
+
+from fastapi import APIRouter, HTTPException, Query
+
+import defi_service
+from models import ApiResponse
+from route_utils import safe
+
+router = APIRouter(prefix="/api/v1/defi")
+
+
+@router.get("/tvl/protocols", response_model=ApiResponse)
+@safe
+async def tvl_protocols() -> ApiResponse:
+    """Get top DeFi protocols ranked by TVL."""
+    data = await defi_service.get_top_protocols()
+    return ApiResponse(data=data)
+
+
+@router.get("/tvl/chains", response_model=ApiResponse)
+@safe
+async def tvl_chains() -> ApiResponse:
+    """Get TVL rankings for all chains."""
+    data = await defi_service.get_chain_tvls()
+    return ApiResponse(data=data)
+
+
+@router.get("/tvl/{protocol}", response_model=ApiResponse)
+@safe
+async def protocol_tvl(protocol: str) -> ApiResponse:
+    """Get current TVL for a specific protocol slug."""
+    tvl = await defi_service.get_protocol_tvl(protocol)
+    if tvl is None:
+        raise HTTPException(status_code=404, detail=f"Protocol '{protocol}' not found")
+    return ApiResponse(data={"protocol": protocol, "tvl": tvl})
+
+
+@router.get("/yields", response_model=ApiResponse)
+@safe
+async def yield_pools(
+    chain: str | None = Query(default=None, description="Filter by chain name"),
+    project: str | None = Query(default=None, description="Filter by project name"),
+) -> ApiResponse:
+    """Get top yield pools, optionally filtered by chain and/or project."""
+    data = await defi_service.get_yield_pools(chain=chain, project=project)
+    return ApiResponse(data=data)
+
+
+@router.get("/stablecoins", response_model=ApiResponse)
+@safe
+async def stablecoins() -> ApiResponse:
+    """Get top stablecoins by circulating supply."""
+    data = await defi_service.get_stablecoins()
+    return ApiResponse(data=data)
+
+
+@router.get("/volumes/dexs", response_model=ApiResponse)
+@safe
+async def dex_volumes() -> ApiResponse:
+    """Get DEX volume overview including top protocols."""
+    data = await defi_service.get_dex_volumes()
+    if data is None:
+        raise HTTPException(
+            status_code=502,
+            detail="Failed to fetch DEX volume data from DefiLlama",
+        )
+    return ApiResponse(data=data)
+
+
+@router.get("/fees", response_model=ApiResponse)
+@safe
+async def protocol_fees() -> ApiResponse:
+    """Get protocol fees and revenue overview."""
+    data = await defi_service.get_protocol_fees()
+    return ApiResponse(data=data)