Artemis Milestone 2e: real connect drives Enable Slot, slot ID correlated

xhci_poll_events()'s Port Status Change connect branch now calls
xhci_cmd_enable_slot() directly (the earlier boot-time smoke test call is
gone), tracked via a new dev->pending_connect_port_id -- since this
driver only ever has one command outstanding at a time, that alone
identifies which port a later Command Completion Event answers, without
needing to match the Command TRB Pointer yet. On success the returned
Slot ID is recorded in a new dev->port_slot_id[], a fixed
uint32_t[XHCI_MAX_TRACKED_PORTS] (32) indexed by port. Disconnect clears
the port's tracked slot (real teardown -- Disable Slot, DCBAA clear,
Section U callback -- is still a later increment).

Fixed array, not heap-allocated: a first attempt sized port_slot_id
dynamically via kmalloc_aligned(dev->max_ports * sizeof(uint32_t), 64)
inside xhci_bringup() and it crashed amd64 with a page fault (IFETCH at
RIP=CR2=0xA0000, the legacy VGA hole) during the unrelated Mama-VM-birth
phase afterward -- a heap-corruption signature, not chased to root cause.
Switching to a fixed array (matching this driver's existing preference
for fixed over dynamic allocation) made the crash go away; the crashing
boot's log is kept (logs/20260822-102516/) as the evidence trail.

Verified live via QMP hotplug, all three architectures: connect ->
"enable slot command submitted" -> "enable slot succeeded", with a
disconnect/reconnect cycle repeating cleanly and no port wedge.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HZ8kNoTuP63pbQtro4qvrm

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