build: the unix paths retire — configuration, logs, and volumes move into the danos tree

/etc/init.csv and /etc/devices.csv become /system/configuration/*.csv (the
repo's etc/ moves to system/configuration/, mirroring the runtime tree),
/var/log becomes /system/logs, and /mnt/usb becomes /volumes/usb. The
kernel VFS gains a carve-out so FAT may serve exactly /system/configuration
and /system/logs beneath the initrd-backed /system while /system and /test
themselves stay unshadowable; FAT's single /var mount splits into those two
rewritten mounts. The kvfs readdir check learns /system's third child and
the ramdisk spawn sweep skips the configuration tree.

Suite 106/106.

library/device/registry/device-registry.zig

@@ -1,4 +1,4 @@
-//! The device registry: parse `/etc/devices.csv` into match rules and bind a
+//! The device registry: parse `/system/configuration/devices.csv` into match rules and bind a
 //! reported device to a driver. This is the data-driven replacement for the
 //! device manager's three hand-written `switch` tables (`pciDriverForIdentity`,
 //! `hidDriverFor`, `usbDriverForIdentity`); the registry is now **authoritative**
@@ -11,7 +11,7 @@
 //! That keeps this module freestanding and unit-testable with plain `zig test`.
 //!
 //! The file format (docs/device-driver-development/device-manager.md, and the
-//! `/etc/devices.csv` header itself): one rule per line, nine comma-separated
+//! `/system/configuration/devices.csv` header itself): one rule per line, nine comma-separated
 //! fields, `#` starts a comment (whole-line or trailing), blank lines ignored.
 //!
 //!     bus, base, class, prog_if, vendor, device, subsystem, hid, driver
@@ -226,7 +226,7 @@ fn parseLine(line: []const u8) Line {
     } };
 }
 
-/// Parse a whole `/etc/devices.csv` into `out_rules`. The string fields of the
+/// Parse a whole `/system/configuration/devices.csv` into `out_rules`. The string fields of the
 /// returned rules point into `source`, which must outlive them.
 pub fn parse(source: []const u8, out_rules: []Rule) ParseResult {
     var result: ParseResult = .{ .count = 0, .malformed = 0, .truncated = false };