Fix: "Clear my history" now clears account history too

clearSession only reset the device-local history; for a signed-in user the panel
shows the account history (serverHistory), which was never cleared and never sent
to the server — so it looked like nothing happened. Add DELETE /api/history
(clear all) and have clearSession reset serverHistory + call it when signed in.

frontend/src/routes/+page.svelte

@@ -124,8 +124,11 @@
     seenIds = new Set();
     dismissed = new Set();
     history = [];
+    serverHistory = [];
     persistSession();
     P.saveJSON(BRIEF_VIEW_KEY, null);
+    // Signed in? Also clear the account (cross-device) history on the server.
+    if (auth.user) delJSON('/api/history').catch(() => {});
     showHistory = false;
     select(selected, true);
   }

goodnews/api.py

@@ -563,6 +563,14 @@ def create_app() -> FastAPI:
             conn.commit()
         return {"ok": True}
 
+    @app.delete("/api/history")
+    def clear_history(request: Request) -> dict:
+        with get_conn() as conn:
+            user = _require_user(conn, request)
+            conn.execute("DELETE FROM user_history WHERE user_id = ?", (user["id"],))
+            conn.commit()
+        return {"ok": True}
+
     @app.delete("/api/history/{article_id}")
     def remove_history(article_id: int, request: Request) -> dict:
         with get_conn() as conn:

tests/test_saved_api.py

@@ -70,3 +70,6 @@ def test_history_and_import(client):
     # granular removal from history
     tc.delete("/api/history/2")
     assert {a["id"] for a in tc.get("/api/history").json()["items"]} == {1, 3}
+    # clear ALL history
+    assert tc.delete("/api/history").json() == {"ok": True}
+    assert tc.get("/api/history").json()["items"] == []