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.

0 files changed, 0 insertions, 0 deletions