Match Wealthfolio accounts by providerAccountId, remap accountId on import

Context: Wealthfolio 3.2 generates its own UUIDs on POST /accounts, ignoring any
`id` we supply. Our logical Account.id lives on as `providerAccountId`, which
WF preserves verbatim.

Live run created six duplicate accounts because ensure_account looked up by
our `id`, never found it, and POSTed a new account on every attempt. Deleted
the duplicates manually via DELETE /accounts/{id}.

This change:
- ensure_account now returns Wealthfolio's UUID; matches existing via
  (provider, providerAccountId)
- pipeline remaps activity.account_id to the WF UUID at submission time
  but keeps dedup keyed on our stable id (WF resets must not blow away
  the whole dedup history)
- test updates to the new account-shape + dedup key expectations

poetry run pytest -q    70 passed
poetry run mypy         clean
poetry run ruff check   clean

broker_sync/sinks/wealthfolio.py

@@ -120,17 +120,30 @@ class WealthfolioSink:
         assert isinstance(raw, list)
         return raw
 
-    async def ensure_account(self, account: Account) -> None:
+    async def ensure_account(self, account: Account) -> str:
+        """Idempotently create the account and return Wealthfolio's UUID for it.
+
+        Wealthfolio generates its own UUIDs on POST /accounts, ignoring any
+        `id` we supply. We identify accounts by (provider, providerAccountId)
+        which Wealthfolio DOES preserve verbatim. Our own Account.id is
+        used as the providerAccountId.
+        """
         existing = await self.list_accounts()
-        if any(a.get("id") == account.id for a in existing):
-            return
-        # Wealthfolio 3.2's NewAccount is camelCase with required booleans.
+        for a in existing:
+            if (
+                a.get("provider") == account.provider
+                and a.get("providerAccountId") == account.id
+            ):
+                wf_id = a.get("id")
+                assert isinstance(wf_id, str)
+                return wf_id
+
+        # NewAccount is camelCase with required booleans.
         # See apps/server/src/models.rs#NewAccount.
         resp = await self._request(
             "POST",
             _ACCOUNTS_PATH,
             json={
-                "id": account.id,
                 "name": account.name,
                 "accountType": str(account.account_type),
                 "currency": account.currency,
@@ -143,6 +156,13 @@ class WealthfolioSink:
             },
         )
         resp.raise_for_status()
+        created = resp.json()
+        wf_id = created.get("id")
+        if not isinstance(wf_id, str):
+            raise WealthfolioError(
+                f"POST /accounts returned no id: {created}"
+            )
+        return wf_id
 
     # -- activity import --