Changes _pending from a single overwriting dict value to a list,
so parallel tool calls each get their own approval slot.
api/routes.py:
- Wraps submit_pending() to append to a list and assign a stable
approval_id (uuid4) to each entry.
- _handle_approval_pending() returns the first queued entry plus
pending_count so the UI can show '1 of N'.
- _handle_approval_respond() pops by approval_id (falls back to
oldest entry for backward-compat with old clients).
- Backward-compat: legacy single-dict values in _pending are
handled without crashing.
static/messages.js:
- respondApproval() sends approval_id in the POST body.
- showApprovalCard() accepts pendingCount, shows '1 of N pending'
counter when multiple approvals are queued.
- _approvalCurrentId tracks the approval_id of the displayed card.
- Poll loop passes pending_count to showApprovalCard.
static/index.html:
- Adds approvalCounter element for the '1 of N' display.
tests/test_approval_queue.py:
- 14 tests: static-analysis checks (Python + JS + HTML),
functional tests that inject two simultaneous approvals and
verify both are surfaced and independently resolvable.
