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.

build.zig

@@ -115,7 +115,8 @@ fn driverArtifact(comptime package: []const u8, comptime artifact: []const u8) S
 
 /// The production ship table — what a plain `zig build` image contains,
 /// beyond the specials the build fn adds around it (init, discovery, the
-/// /etc data files; the /test fixtures join only under -Dtest-case).
+/// /system/configuration data files; the /test fixtures join only under
+/// -Dtest-case).
 /// Selecting what goes into a build = selecting rows: a package in no row is
 /// not just unshipped, its build file is never even loaded
 /// (docs/build-packages-plan.md).
@@ -265,9 +266,9 @@ pub fn build(b: *std.Build) void {
     // (receives the root's -Dserial as a dependency option — its liveness
     // heartbeat is a serial/test-build diagnostic the QEMU harness asserts
     // on; a flashable image leaves it out), discovery (the -Ddiscovery pick),
-    // and the /etc data files. Each binary builds itself against the domain
-    // packages via build-support's shared recipe; the root just takes
-    // artifacts (docs/build-packages-plan.md).
+    // and the /system/configuration data files. Each binary builds itself
+    // against the domain packages via build-support's shared recipe; the root
+    // just takes artifacts (docs/build-packages-plan.md).
     var bundled_list: std.ArrayListUnmanaged(images.BundledBinary) = .empty;
     bundled_list.append(b.allocator, .{
         .path = "system/services/init",
@@ -300,15 +301,16 @@ pub fn build(b: *std.Build) void {
             .binary = b.dependency(row.package, .{}).artifact(row.artifact).getEmittedBin(),
         }) catch @panic("OOM");
     }
-    // Data files, not binaries: packing them under /etc makes the kernel
-    // auto-mount /etc as a read-only initrd tree (system/kernel/vfs.zig
+    // Data files, not binaries: packing them under /system/configuration rides
+    // the kernel's read-only initrd mount of /system (system/kernel/vfs.zig
     // setInitialRamdisk) — the device manager reads its registry and init its
     // service list with no filesystem service running. -Ddiagnose selects the
     // init.csv variant that omits the display stack (so the kernel's boot
-    // transcript stays on screen); both bundle at the same /etc/init.csv path.
-    const init_csv_source = if (diagnose) "etc/init-diagnose.csv" else "etc/init.csv";
-    bundled_list.append(b.allocator, .{ .path = "etc/devices.csv", .binary = b.path("etc/devices.csv") }) catch @panic("OOM");
-    bundled_list.append(b.allocator, .{ .path = "etc/init.csv", .binary = b.path(init_csv_source) }) catch @panic("OOM");
+    // transcript stays on screen); both bundle at the same
+    // /system/configuration/init.csv path.
+    const init_csv_source = if (diagnose) "system/configuration/init-diagnose.csv" else "system/configuration/init.csv";
+    bundled_list.append(b.allocator, .{ .path = "system/configuration/devices.csv", .binary = b.path("system/configuration/devices.csv") }) catch @panic("OOM");
+    bundled_list.append(b.allocator, .{ .path = "system/configuration/init.csv", .binary = b.path(init_csv_source) }) catch @panic("OOM");
     // A no-option build assumes neither -Dtest-case nor -Ddiagnose: it ships the
     // production set only. The userspace test fixtures under /test join in only
     // for a test build — which the QEMU harness signals by passing