fix: /posts source filter, /performance closed_at basis, funding venue field

- /posts gains an optional ?source= filter. The Macro page was pulling the
  latest-500 posts globally and filtering client-side; rare scanner signals
  (btc_bottom_reversal ~2-4/cycle, funding_reversal hourly) got pushed off the
  page by frequent Trump posts, so Macro falsely showed "no signals".
- /performance now filters and orders by closed_at (realized-PnL-in-window)
  instead of opened_at, so it shares ONE basis with the frontend Analytics
  page (which filters every window by closed_at). Boundary trades no longer
  land in one basis but not the other.
- funding snapshot returns the actual `venue` (provider.name) so the frontend
  label follows the real data source instead of hardcoding "Binance".

72 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/api/posts.py

@@ -74,13 +74,21 @@ async def get_posts(
     request: Request,
     limit: int = Query(default=20, ge=1, le=500),
     page: int = Query(default=1, ge=1),
+    source: Optional[str] = Query(
+        default=None,
+        description="Filter to a single source (e.g. 'btc_bottom_reversal', "
+                    "'funding_reversal', 'truth'). Without it, rare-source "
+                    "signals can be pushed off the latest-N page by Trump posts.",
+    ),
     db: AsyncSession = Depends(get_db),
     response: Response = None,
 ):
     offset = (page - 1) * limit
-    result = await db.execute(
-        select(Post).order_by(Post.published_at.desc()).offset(offset).limit(limit)
-    )
+    stmt = select(Post)
+    if source:
+        stmt = stmt.where(Post.source == source)
+    stmt = stmt.order_by(Post.published_at.desc()).offset(offset).limit(limit)
+    result = await db.execute(stmt)
     posts = result.scalars().all()
     # Posts are scraped every 5s but rarely change once written — allow CDN/browser
     # to cache for 30s. stale-while-revalidate=60 means stale content is served