C2: migrate consumers off the runtime shim to direct concern-module imports

Every user binary and the two device-logic library modules (pci, usb) now
`@import` the concern modules directly instead of aliasing through `runtime`:

  runtime.ipc/process/time/service/input/block/display  -> @import("<module>")
  runtime.device / runtime.device_manager               -> @import("driver")
  runtime.fs                                             -> @import("file-system")
  runtime.Thread                                         -> @import("thread").Thread
  runtime.system.{write,writeRecord,klog*}              -> logging.*
  runtime.system.{sleep,timerOnce,wallClock,clock}     -> time.*
  runtime.system.{spawn*,kill,exit,yield,processes,...}-> process.*
  runtime.system.{mmap,munmap,PROT_*}                  -> memory.*
  runtime.dma.* / runtime.shared_memory.* / runtime.allocator -> memory.*

Each consumer keeps its own alias name (e.g. `const device = @import("driver")`),
so call sites are unchanged and there are no collisions with local `driver`
variables. build.zig now injects the concern modules into every user binary via
`default_imports`; pci/usb module import lists were updated to match.

The `runtime` and `system` shims remain for one more step (root.zig still uses
runtime); they are deleted in C5. Nothing but root.zig imports `runtime` now.

Verified: zig build, zig build test, and 17 QEMU cases (smoke, device-manager,
logger, fat-mount, fat-mutations, usb-storage, usb-hid, display-native,
virtio-gpu, input, thread-spawn, thread-mutex, process-kill, shared-memory,
driver-restart, acpi-ps2, pci-scan).

system/services/vfs-test/vfs-test.zig

@@ -1,5 +1,5 @@
 //! /system/tests/vfs-test — a ring-3 client that proves the kernel VFS end to
-//! end through the plain `runtime.fs` API: resolve its OWN binary under the
+//! end through the plain `file_system` API: resolve its OWN binary under the
 //! kernel-served /system mount, check its metadata, read its ELF magic, and
 //! list /system/services. On success it heartbeats "vfstest: ok" so the kernel
 //! test can observe it; on failure it reports what went wrong.
@@ -9,10 +9,12 @@
 //! server's release-on-death sweep are the point.
 
 const std = @import("std");
-const runtime = @import("runtime");
-const fs = runtime.fs;
+const fs = @import("file-system");
+const process = @import("process");
+const time = @import("time");
+const logging = @import("logging");
 
-pub fn main(init: runtime.process.Init) void {
+pub fn main(init: process.Init) void {
     if (init.arguments.count > 1) {
         park();
         return;
@@ -21,30 +23,30 @@ pub fn main(init: runtime.process.Init) void {
     // Our own binary, resolved through the kernel mount table.
     const self_path = "/system/tests/vfs-test";
     var file = fs.open(self_path, .{}) orelse {
-        _ = runtime.system.write("vfstest: open of own binary failed\n");
+        _ = logging.write("vfstest: open of own binary failed\n");
         return;
     };
     defer file.close();
 
     const attributes = file.attributes() orelse {
-        _ = runtime.system.write("vfstest: attributes failed\n");
+        _ = logging.write("vfstest: attributes failed\n");
         return;
     };
     if (attributes.kind != .regular or attributes.size == 0) {
-        _ = runtime.system.write("vfstest: bad attributes\n");
+        _ = logging.write("vfstest: bad attributes\n");
         return;
     }
 
     var header: [4]u8 = undefined;
     const n = file.read(&header) orelse 0;
     if (n != 4 or header[0] != 0x7f or header[1] != 'E' or header[2] != 'L' or header[3] != 'F') {
-        _ = runtime.system.write("vfstest: ELF magic mismatch\n");
+        _ = logging.write("vfstest: ELF magic mismatch\n");
         return;
     }
 
     // The write refusal: /system is read-only by construction.
     if (file.write("x") != null or fs.open("/system/tests/new-file", .{ .create = true }) != null) {
-        _ = runtime.system.write("vfstest: /system accepted a write\n");
+        _ = logging.write("vfstest: /system accepted a write\n");
         return;
     }
 
@@ -59,13 +61,13 @@ pub fn main(init: runtime.process.Init) void {
         }
     }
     if (!saw_init) {
-        _ = runtime.system.write("vfstest: /system/services listing missed init\n");
+        _ = logging.write("vfstest: /system/services listing missed init\n");
         return;
     }
 
     while (true) {
-        _ = runtime.system.write("vfstest: ok\n");
-        runtime.system.sleep(1000);
+        _ = logging.write("vfstest: ok\n");
+        time.sleepMillis(1000);
     }
 }
 
@@ -76,14 +78,14 @@ fn park() void {
     var tries: u32 = 0;
     while (parked == null and tries < 1000) : (tries += 1) {
         parked = fs.open("/mnt/usb/parked", .{ .create = true });
-        if (parked == null) runtime.system.sleep(20);
+        if (parked == null) time.sleepMillis(20);
     }
     if (parked == null) {
-        _ = runtime.system.write("vfstest: park open failed\n");
+        _ = logging.write("vfstest: park open failed\n");
         return;
     }
     while (true) {
-        _ = runtime.system.write("vfstest: parked\n");
-        runtime.system.sleep(500);
+        _ = logging.write("vfstest: parked\n");
+        time.sleepMillis(500);
     }
 }