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>

decisions/questions-process.md

@@ -175,7 +175,7 @@ The findings file separates the agent's reasoning from its authority. Binary gat
 
 **Related:**
 - `feedback_broken_tests_not_preexisting_shield.md` — pattern sprints may enable
-- `team-test.md` — Claude Code harness test results (tmux teams partially broken v2.1.123)
+- tmux teammate mode: confirmed working on Claude Code 2.1.148 (the earlier "broken" status was a `teammateMode: in-process` config issue, not a regression)
 - Epic #854 — pipeline discipline automation
 - D-166 — cascade phases