Feature: USB - Hotplug, mass storage, disconnect callbacks, dynamic device lists

- Add disconnect callback (fnDisconnect) to TUSBDevice for safe unplug handling
- Add HotplugArmed/PortChangePending flags to TUSBHCDriver for deferred
  hotplug processing from ISR context (OHCI RHSC, EHCI PCD, xHCI PSC)
- Implement usb_rescan_port() and usb_check_hotplug() in usbcore
- Add usb_bulk_transfer_wait() with timer-based timeout (bios_data_area)
- Add timer-based timeout to usb_control_msg polling loop
- Replace static device arrays with dynamic linked lists in class drivers:
  usb_keyboard (KeyboardList), usb_mouse (MouseList), usb_storage (StorageList)
- Add 3-strike fail-count self-deactivation in keyboard/mouse poll loops
- Add unload() disconnect handlers for keyboard, mouse, and storage drivers
- Implement USB Mass Storage BOT driver (usb_storage.pas):
  CBW/CSW transport, SCSI INQUIRY/READ_CAPACITY/READ10/WRITE10,
  storagemanagement integration with read/write callbacks
- xHCI: acknowledge port status change W1C bits in event handler
- Integrate usb_check_hotplug + poll_keyboards/poll_mice into kernel main loop

src/driver/bus/usb/EHCI.pas

@@ -1355,6 +1355,10 @@ begin
 
         { Process completions (walks QH lists) }
         ehci_poll(hc);
+
+        { Hotplug: if Port Change Detect, flag for deferred processing }
+        if ((usbsts AND EHCI_STS_PCD) <> 0) and hc^.HotplugArmed then
+            hc^.PortChangePending := true;
     end;
     usbcore.fire_completion_hooks;
 end;

src/driver/bus/usb/OHCI.pas

@@ -1058,6 +1058,10 @@ begin
 
         { Process completions (walks ED lists) }
         ohci_poll(hc);
+
+        { Hotplug: if RootHubStatusChange, flag for deferred processing }
+        if ((intSts AND OHCI_INT_RHSC) <> 0) and hc^.HotplugArmed then
+            hc^.PortChangePending := true;
     end;
     usbcore.fire_completion_hooks;
 end;

src/driver/bus/usb/USB.pas

@@ -35,6 +35,7 @@ uses
     usbhub,
     usb_keyboard,
     usb_mouse,
+    usb_storage,
     OHCI, UHCI, EHCI, XHCI;
 
 procedure init;
@@ -89,6 +90,9 @@ begin
     { Initialize HID class drivers }
     usb_keyboard.init;
     usb_mouse.init;
+
+    { Initialize storage class driver }
+    usb_storage.init;
     
     UHCI_ID.Bus:= biPCI;
     UHCI_ID.id0:= idANY;

src/driver/bus/usb/XHCI.pas

@@ -1870,6 +1870,8 @@ var
     pend      : PXHCI_PendingTransfer;
     transfer  : PUSBTransfer;
     processed : boolean;
+    hpPortId  : uint8;
+    hpPortSC  : uint32;
 begin
     if (hc = nil) or (hc^.PrivData = nil) then exit;
     priv := PXHCI_PrivData(hc^.PrivData);
@@ -1924,9 +1926,19 @@ begin
             end;
 
             XHCI_TRB_PORT_STATUS_CHG: begin
-                { Port ID in bits 31:24 of Param0 }
+                { Port ID in bits 31:24 of Param0 (1-based) }
+                hpPortId := uint8((evt.Param0 SHR 24) AND $FF);
                 syslog.log('XHCI', 'Port Status Change: port ');
-                syslog.writeintln((evt.Param0 SHR 24) AND $FF);
+                syslog.writeintln(hpPortId);
+                if hpPortId > 0 then begin
+                    { Acknowledge port status change by writing W1C bits }
+                    hpPortSC := xhci_readl(priv^.OpBase, XHCI_OP_PORTSC_BASE + ((hpPortId - 1) * $10));
+                    xhci_writel(priv^.OpBase, XHCI_OP_PORTSC_BASE + ((hpPortId - 1) * $10),
+                        (hpPortSC AND $0E00C3E0) OR $00FE0000);
+                    { Flag for deferred hotplug processing }
+                    if hc^.HotplugArmed then
+                        hc^.PortChangePending := true;
+                end;
             end;
         end;
     end;

src/driver/bus/usb/usbtypes.pas

@@ -217,6 +217,9 @@ type
     PUSBHCDriver = ^TUSBHCDriver;
     PUSBTransfer = ^TUSBTransfer;
 
+    { ---- Disconnect Callback ---- }
+    TUSBDisconnectCallback = procedure(dev : PUSBDevice);
+
     { ---- Transfer Request ---- }
 
     TUSBTransfer = record
@@ -246,6 +249,7 @@ type
         Endpoints    : array[0..USB_MAX_ENDPOINTS-1] of TUSBEndpoint;
         NumEndpoints : uint8;
         Configured   : boolean;
+        fnDisconnect : TUSBDisconnectCallback; { Called before device is freed on unplug }
     end;
 
     { ---- HC Driver Abstraction (Function Pointer Types) ---- }
@@ -269,6 +273,8 @@ type
         PrivData     : Pointer;     { HC-specific state }
         Devices      : PLinkedListBase; { List of PUSBDevice attached }
         NextAddress  : uint8;       { Next available USB address (1-127) }
+        PortChangePending : boolean; { Set by ISR when port status changes; processed in deferred context }
+        HotplugArmed : boolean;     { False during boot; set true after initial scan_ports to ignore spurious RHSC }
         { Operations }
         fnReset      : TUSBHCReset;
         fnStart      : TUSBHCStart;