establishment: block stops being a name, and enumerate learns to page

P2 of docs/establishment-planes-plan.md. usb-storage serves nameless — one
process per stick cannot share an exclusive bind, and a second stick used to
die silently on -EBUSY before ever helloing. Its one hello now moves both
directions at once: the block-serving endpoint up, its controller channel
down. fat finds its volume through the manager — a new `.consumer` role asks
for the channel of the driver BOUND TO a device (distinct from the device's
reporter), found by enumerating the tree for the mass-storage identity.
fat stays single-volume; the boot-volume-by-content choice is M21.

The conversion immediately caught a live truncation of exactly the audit's
shape: ChildEntry grew to 32 bytes, one enumerate reply holds ~7, and a real
tree carries a dozen ACPI nodes before the first USB child — the storage
entry silently never fit (the protocol comment already said "paging joins
the protocol if a tree ever outgrows one packet"). enumerate is now paged:
Header.target is the start cursor, a short page is the end; device-list's
page-0 read is unchanged.

Grant rows move with the code: the block bind and fat's block open die, fat
gains open device-manager. Gate: 18 cases green including the registry
trio, device-list, and both IOMMU storage variants.

system/drivers/usb-hid/keyboard.zig

@@ -77,7 +77,7 @@ pub fn main(init: process.Init) void {
 
     // The hello both meets the spawn deadline and brings back the channel to
     // THIS device's controller — routed by lineage, never found by name.
-    const bus = device_manager.helloForChannel(.device, device_id) orelse return;
+    const bus = device_manager.helloForChannel(.device, device_id, null) orelse return;
     var device = usb.open(bus, device_id) orelse {
         std.log.info("could not open device {d}", .{device_id});
         return;

system/drivers/usb-hid/mouse.zig

@@ -43,7 +43,7 @@ pub fn main(init: process.Init) void {
 
     // The hello both meets the spawn deadline and brings back the channel to
     // THIS device's controller — routed by lineage, never found by name.
-    const bus = device_manager.helloForChannel(.device, device_id) orelse return;
+    const bus = device_manager.helloForChannel(.device, device_id, null) orelse return;
     var device = usb.open(bus, device_id) orelse {
         std.log.info("could not open device {d}", .{device_id});
         return;