T23c round 2 fix

- a trigger opens only its word, so a path keeps its slashes in the query
- suggestions reveal the cursor once the list has its bounds: Popup takes a
  row to reveal, and a canvas inside the list asks for it and one more frame

TASKS.md

@@ -262,3 +262,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T23b | 2 | FAIL | the gallery's narrow passage built a vec of one range, which clippy refuses, so the checks failed |
 | T23b | 3 | PASS | |
 | T23c | 1 | FAIL | suggestion arrows landed on disabled rows and left the cursor out of view; a dot ended a file mention; the drop veil never showed, since gpui styles a drag-over only on an element with a hitbox; a parameter's places came from its step alone; the gallery's prompt menu and Reset only logged |
+| T23c | 2 | FAIL | a slash inside a path read as a new trigger, closing the file suggestions; a list whose first rows were disabled opened with its cursor out of view |