chore(meta): retire obsolete team-test.md and update references

The tmux teammate-mode investigation is resolved (works on 2.1.148; the
'broken regression' was a teammateMode: in-process config issue). Per the
file's own cleanup note, delete it now that the test passes.

Update the two references:
- decisions/questions-process.md: replace the stale 'partially broken'
  pointer with the resolved status.
- whats-next/SKILL.md: the 'custom subagent_types lose SendMessage' caveat is
  fixed (all agents now carry SendMessage + Task tools), so reword and drop
  the dead team-test.md link.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/skills/whats-next/SKILL.md

@@ -93,7 +93,9 @@ Wait for user confirmation before proceeding to Step 2.
 
 Spawn one Si agent per ticket in the confirmed batch, running in parallel.
 Use `general-purpose` subagent_type with Si's personality baked into the
-prompt (custom subagent_types lose SendMessage — see team-test.md).
+prompt. (The `si` subagent_type now works directly too — all agent
+definitions carry the team coordination tools, SendMessage + Task, as of the
+agent-teams tooling fix; they load at lead startup.)
 
 For each ticket, spawn: