feat(settings): add a tool approval mode with an explicit off (YOLO) option (#6304)

* feat: add optional tool approval mode

Admin-configurable tool_approval_mode setting (ask/auto) for the
post-external-context tool approval gate.

- ask (default): existing approval flow, gate stays on
- auto: bypasses the approval gate for all runs - same effect as
  ODYSSEUS_TOOL_APPROVAL_GATE=0. Documented honestly in the settings
  row copy and in THREAT_MODEL.md, per review on #6304.
- value validated server-side ({ask, auto}, anything else -> 400)
- no new env var: the setting wires to the existing gate control
- tests: setting validation + _tool_approval_gate_bypassed behavior

* feat: surface deployment gate state on Tool approval row

Follow-up to StressTestor's re-review: when ODYSSEUS_TOOL_APPROVAL_GATE is
set to a falsy value, the Tool approval row still read 'Always ask' even though
the gate was off, misleading admins the other way.

GET /api/auth/settings now returns tool_approval_gate_env_disabled (derived
from TOOL_APPROVAL_GATE_ENABLED) for admins, and the settings row renders a
red notice naming the env var and explaining that the gate is off for every
run regardless of the stored setting. Non-admin/scrubbed responses do not
expose the deployment state. Test covers both env values and the scrub path.

* refactor: rename tool approval mode auto to off

The gate-off value is now "off" ("Off (YOLO)" in the UI) so the auto-approve name stays available for the future judged mode.

---------

Co-authored-by: Matej <matej@local>

tests/test_tool_approval_task_scope.py

@@ -340,7 +340,7 @@ def test_route_context_agent_frontend_and_cache_bust_wire_the_contract():
     assert "_without_latest_matching_user_message(" not in helpers
     assert "selected_tools=approval_selected_tools" in agent
     assert "continuation_query=_retrieval_query or _last_user" in agent
-    assert "approval_gate_bypassed=bool(" in agent
+    assert "approval_gate_bypassed=_tool_approval_gate_bypassed(" in agent
     assert "['approve', 'approve_task', 'deny']" in frontend
     assert "input.value = label" not in frontend
     assert "const msg = approvalForSend ? '' : el('message').value;" in frontend