refactor(ai-vterm): retire M-F9 buffer picker; bind to cj/toggle-gptel

M-F9 used to invoke `cj/ai-vterm-pick-buffer' (a buffer picker
narrowed to alive AI-agent buffers).  In practice the F9 plain-key
toggle + C-F9 project picker covered the common cases, and the
buffer picker rarely earned its keystroke.  Rebind M-F9 to
`cj/toggle-gptel' so the F9 family covers the two main in-Emacs AI
surfaces at one keystroke each:

  <f9>    ai-vterm toggle      (unchanged)
  C-<f9>  ai-vterm picker      (unchanged)
  M-<f9>  gptel *AI-Assistant* (NEW)

Removed entirely:
- `cj/ai-vterm-pick-buffer' (the command itself).
- `cj/--ai-vterm-pick-buffer-candidates' (its helper).
- `tests/test-ai-vterm--pick-buffer-candidates.el' (deleted).

Updated:
- `tests/test-ai-vterm--f9-in-vterm.el' binding assertions
  (vterm-mode-map and global) flipped to `cj/toggle-gptel'.
- Module commentary + `cj/ai-vterm' docstring describe the new
  M-F9 behavior.
- `cj/toggle-gptel' lives in `modules/ai-config.el'; the binding
  stays in `ai-vterm.el' next to the rest of the F9 family so the
  dispatch shape is visible in one place.

1 files changed, 9 insertions, 4 deletions

diff --git a/tests/test-ai-vterm--f9-in-vterm.el b/tests/test-ai-vterm--f9-in-vterm.el
index 1355bd6a..ff8939c8 100644
--- a/tests/test-ai-vterm--f9-in-vterm.el
+++ b/tests/test-ai-vterm--f9-in-vterm.el
@@ -24,19 +24,24 @@
   (should (eq (keymap-lookup vterm-mode-map "<f9>") #'cj/ai-vterm)))
 
 (ert-deftest test-ai-vterm-f9-family-bound-in-vterm-mode-map ()
-  "Normal: the C-/M- F9 variants are bound in `vterm-mode-map' too."
+  "Normal: the C-/M- F9 variants are bound in `vterm-mode-map' too.
+`M-<f9>' toggles gptel's *AI-Assistant* window (rebound here from
+the old `cj/ai-vterm-pick-buffer' command, which was removed)."
   (should (eq (keymap-lookup vterm-mode-map "C-<f9>") #'cj/ai-vterm-pick-project))
-  (should (eq (keymap-lookup vterm-mode-map "M-<f9>") #'cj/ai-vterm-pick-buffer)))
+  (should (eq (keymap-lookup vterm-mode-map "M-<f9>") #'cj/toggle-gptel)))
 
 (ert-deftest test-ai-vterm-f9-not-self-insert-in-vterm ()
   "Boundary: vterm's default <f9> -> `vterm--self-insert' was overridden."
   (should-not (eq (keymap-lookup vterm-mode-map "<f9>") 'vterm--self-insert)))
 
 (ert-deftest test-ai-vterm-f9-still-bound-globally ()
-  "Normal: the global F9 family bindings are intact."
+  "Normal: the global F9 family bindings are intact.
+`<f9>' toggles the ai-vterm agent window; `C-<f9>' picks a project
+agent; `M-<f9>' toggles gptel's *AI-Assistant* window (rebound from
+the retired `cj/ai-vterm-pick-buffer')."
   (should (eq (lookup-key (current-global-map) (kbd "<f9>")) #'cj/ai-vterm))
   (should (eq (lookup-key (current-global-map) (kbd "C-<f9>")) #'cj/ai-vterm-pick-project))
-  (should (eq (lookup-key (current-global-map) (kbd "M-<f9>")) #'cj/ai-vterm-pick-buffer)))
+  (should (eq (lookup-key (current-global-map) (kbd "M-<f9>")) #'cj/toggle-gptel)))
 
 (provide 'test-ai-vterm--f9-in-vterm)
 ;;; test-ai-vterm--f9-in-vterm.el ends here