Update stale /sbin/ references to real FHS paths

The reorg moved user binaries under /system (init -> /system/services/init,
drivers -> /system/drivers/<name>, vfs-test -> /system/services/vfs/vfs-test), but
many comments and log strings still named the old /sbin/ home. Retarget them all:
kernel/loader/test comments and the two boot log lines, plus vision.md and the
driver-model.md proposed tree (also dropped the stale `d` suffixes and rt->runtime
there). The initial-ramdisk spawn log no longer fakes a /sbin/ prefix, since those
binaries live in different homes (services vs drivers).

Left the FSH design doc's /sbin and /lib rows alone — whether /sbin stays a
directory at all is a design call for its owner, not a stale-comment fix.

system/drivers/hpet/hpet.zig

@@ -1,4 +1,4 @@
-//! /sbin/hpet — a user-space HPET driver. It proves the whole driver model end to
+//! /system/drivers/hpet — a user-space HPET driver. It proves the whole driver model end to
 //! end: enumerate the device table, find the HPET, claim it, map its registers into
 //! this ring-3 address space (strong-uncacheable), **bind its interrupt to an IPC
 //! endpoint**, then sit blocked in `replyWait` until the hardware wakes it.