fix(ci3): accept slashes in /list/<path:key> for merge-train history (#23160)

## Summary

Test logs print a **History** link like
`…/list/history_<hash>_<TARGET_BRANCH>`. For
`TARGET_BRANCH=merge-train/spartan` the URL contains a `/`, and Flask's
default `/list/<key>` converter only matches a single path segment, so
the link 404s. Percent-encoding (`%2F`) doesn't help: WSGI (gunicorn)
URL-decodes `PATH_INFO` per PEP 3333, so by the time Werkzeug routes the
request, the `%2F` is already a `/`.

Fix: change the route to `/list/<path:key>`, which matches slashes. This
makes the existing history links work — and recovers all data already
written to Redis under keys like `history_<hash>_merge-train/spartan`
(history tracking for `merge-train/*` is already enabled by the existing
condition in `ci3/run_test_cmd`).

This commit reverts the earlier producer-side sanitization in
`ci3/run_test_cmd` / `ci3/exec_test`. Doing it in the producer would
leave existing entries orphaned under the old slash keys; the
dashboard-side fix avoids the split.

Note: dashboard changes ship via `ci3/dashboard/deploy.sh` (manual rsync
+ `systemctl restart rkapp`).

Reproducer: http://ci.aztec-labs.com/54e749c45512a629 → click
**History**.

Background:
https://gist.github.com/AztecBot/33fcdd84eba7b273d3f67dfd2ad6be8f

## Test plan

- [ ] After `ci3/dashboard/deploy.sh`, the History link on a test run on
a `merge-train/*` PR resolves to the existing list.
- [ ] Existing `/list/<key>` URLs without slashes (e.g. `…_next`,
`…_v4`) continue to work.

Author: AztecBot

ci3/dashboard/rk.py

@@ -403,7 +403,11 @@ def show_section(section):
         follow='top'
     )
 
-@app.route('/list/<key>')
+# <path:key> (not <key>) so branch-qualified history keys like
+# `history_<hash>_merge-train/spartan` route correctly. WSGI decodes %2F to /
+# in PATH_INFO before Flask routes, so percent-encoding can't rescue a plain
+# <key> converter — only <path:key> matches segments containing /.
+@app.route('/list/<path:key>')
 @optional_auth
 def get_list(key):
     value = get_list_as_string(key)