Rework the avo:skills install into a screen-per-question panel

Adrian's feedback on the 4.1.1 panel: everything was on one screen, moving
the highlight and pressing enter kept the first option (space was required
and easy to miss), and once you moved past a group there was no way back.

One question per screen now. A radio's selection follows the cursor, so
moving is choosing; a checkbox keeps space as the toggle. Left arrow goes
back and keeps what was already answered. Screens that do not apply are
skipped — the link question only appears once more than one directory is
picked, the cleanup questions only when there is something to remove.

Nothing is written until a final confirm screen lists what is about to
happen, including both removals.

Removing leftovers is a question rather than a printed suggestion, and the
project and ~/.claude/skills are asked separately: that second directory is
shared with every other project on the machine and deserves its own yes.

Picking several agent directories now writes one real file and relative
symlinks from the rest, so refreshing the loader is a single edit and the
directories cannot drift apart. .agents/skills holds the file, being the
vendor-neutral one. A filesystem that cannot symlink is detected, and the
write falls back to a copy rather than failing.

The generator takes no flags at all. A flag per question is a second
surface to document and keep in step with the screens; there is one way to
run this and it asks. A run with no terminal — piped, or the suite —
installs the recommended answers and removes nothing, since nobody was
there to decline a delete.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Paul-Bob

.gitignore

@@ -81,3 +81,8 @@ brakeman_results.html
 .env
 .env.test
 *~
+
+# Written by `rails g avo:skills`, by hand or from its specs. Generated output.
+spec/dummy/.agents/
+spec/dummy/.claude/
+spec/dummy/.cursor/