Add imap-ingest CLI + ImapProvider: route emails to IE/Schwab parsers

Wires the IE + Schwab email parsers into an actual runnable sync. Walks
the IMAP mailbox, routes each message by sender domain:
  - *@investengine.com → invest_engine.parse_invest_engine_email
  - *@schwab.com       → schwab.parse_schwab_email
then pushes the resulting Activities through the shared pipeline.

broker-sync imap-ingest — new CLI command taking IMAP_HOST/USER/PASSWORD/
DIRECTORY (mirrors the old wealthfolio-sync image's env shape so the
Terraform CronJob's existing env wiring works unchanged).

Verified: poetry run pytest -q → 109 passed + 1 skipped; mypy strict
clean (37 files); ruff + yapf clean.

tests/sinks/test_wealthfolio.py

@@ -48,7 +48,10 @@ def _login_ok(req: httpx.Request) -> httpx.Response:
     assert body == {"password": "hunter2"}
     return httpx.Response(
         200,
-        json={"authenticated": True, "expiresIn": 604800},
+        json={
+            "authenticated": True,
+            "expiresIn": 604800
+        },
         headers={"set-cookie": "wf_token=abc123; Path=/api; HttpOnly"},
     )
 
@@ -219,21 +222,25 @@ async def test_import_dry_run_then_real(tmp_path: Path) -> None:
         calls.append(req.url.path)
         if req.url.path == "/api/v1/activities/import/check":
             # /import/check hydrates and returns a list of ActivityImport.
-            return httpx.Response(200, json=[
-                {
-                    "symbol": "VUAG",
-                    "isValid": True,
-                    "errors": None,
-                    "assetId": "enriched-asset-uuid",
-                    "exchangeMic": "XLON",
-                },
-            ])
+            return httpx.Response(200,
+                                  json=[
+                                      {
+                                          "symbol": "VUAG",
+                                          "isValid": True,
+                                          "errors": None,
+                                          "assetId": "enriched-asset-uuid",
+                                          "exchangeMic": "XLON",
+                                      },
+                                  ])
         if req.url.path == "/api/v1/activities/import":
             return httpx.Response(
                 200,
                 json={
                     "activities": [
-                        {"id": "wf-1", "external_id": "t212:1"},
+                        {
+                            "id": "wf-1",
+                            "external_id": "t212:1"
+                        },
                     ],
                 },
             )