feat(retrieval): a menu line is a name, its kind and System, and the whole passage that matched (#4364)

Injected lines rendered a snippet's or lesson's title, which carries its
whole trigger by construction (the embedding shape) and ran past 1,500
characters -- again on every `seen` repeat. The passage under a line was
cut to 200 chars from the middle, keeping its head (the title again) and
losing where the match was.

Now, on both the prompt menu and the write-path prior-art menu:
- the line shows the record's NAME (snippet data.name / lesson subject),
  with its kind and System (`[issue (done) · Plugin & hooks]`);
- the passage is the whole matched chunk, title prefix stripped, on one
  line so the blockquote holds; a title-only match hands over the trigger;
- a `seen` record is a one-line pointer to what is already in context.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/conftest.py

@@ -102,6 +102,20 @@ def _no_supersession():
         yield
 
 
+@pytest.fixture(autouse=True)
+def _no_system_labels():
+    """Stub the menu's "which System is each line about?" lookup (#4364).
+
+    Autouse because every test that renders an injected menu reaches it, and
+    it is a real database call on a path those tests run without one. Stubbed
+    to "no labels", the state of any untagged record. Tests of the label
+    itself patch it with a value.
+    """
+    with patch("scribe.services.plugin_context.system_names_for",
+               AsyncMock(return_value={})):
+        yield
+
+
 @pytest.fixture(autouse=True)
 def _no_task_log_arm():
     """Stub the task-log read arm that get_task / list_tasks / get_milestone