feat: email design & copy upgrade for all 9 transactional emails

Redesigned _email_wrap(): lowercase wordmark header matching website,
3px blue accent border, preheader text support, HR separators.
_email_button() now full-width block for mobile tap targets.

Rewrote copy: improved subject lines, urgency cues, quick-start links
in welcome, styled project recap in quote verify, heat badges on lead
forward, "what happens next" in lead matched, secondary CTAs.

~30 new/updated translation keys in both EN and DE.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/tests/test_waitlist.py

@@ -199,7 +199,7 @@ class TestWorkerTask:
             mock_send.assert_called_once()
             call_args = mock_send.call_args
             assert call_args.kwargs["to"] == "entrepreneur@example.com"
-            assert "launching soon" in call_args.kwargs["subject"].lower()
+            assert "notify you at launch" in call_args.kwargs["subject"].lower()
             assert "waitlist" in call_args.kwargs["html"].lower()
 
     @pytest.mark.asyncio