Post-reorg cleanup: POSIX layer, and naming fixes

Follow-up to the monorepo re-org. Suite 35/35 plus host tests green.

POSIX compatibility is now its own library, library/posix/ (unistd, stdio),
layered strictly over the runtime — it calls the runtime's IPC/heap, never
system calls directly. The runtime is now POSIX-free (the danos-native
application ABI). The VFS wire protocol is danos-native throughout
(Stat -> FileStatus, .stat -> .status, O_CREAT -> create); the POSIX layer
maps the POSIX spellings at the boundary. The coding standard's ABI-name
exception is scoped to one place: a file is allowed POSIX spellings only if it
lives under library/posix/ — everywhere else, danos naming with no exception.

Naming fixes, all mechanical:
- initrd -> initial-ramdisk: the source file, the module, the tool
  (make-initial-ramdisk.py), the artifact (initial-ramdisk.img, including the
  bootloader's load path), and the identifiers.
- system/kernel/device-service.zig -> devices-broker.zig: it is ring-0 kernel
  code (the trusted device table + claim capability), not a ring-3 service. The
  future user-space device *manager* (policy) will live in system/services/.
- Dropped the daemon `d` suffix: hpetd -> hpet, busd -> bus. A driver lives in
  system/drivers/, so the folder already says what it is; encoding the role in
  the name too is redundant. The coding standard drops that exception.
- system/devices/aml/interp.zig -> interpreter.zig (the type was already
  Interpreter).

system/kernel/main.zig

@@ -8,9 +8,9 @@ const pmm = @import("pmm.zig");
 const heap = @import("heap.zig");
 const scheduler = @import("scheduler.zig");
 const process = @import("process.zig");
-const device_service = @import("device-service.zig");
+const devices_broker = @import("devices-broker.zig");
 const irq = @import("irq.zig");
-const initrd = @import("initrd");
+const initial_ramdisk = @import("initial-ramdisk");
 const platform = @import("platform");
 const tests = @import("tests.zig");
 const build_options = @import("build_options");
@@ -161,10 +161,10 @@ fn kmain(boot_information: *const BootInformation) noreturn {
 
         // Snapshot the device tree for user-space drivers (device_enumerate/claim/
         // mmio_map operate on this flat, id-indexed table + claim map).
-        device_service.init(&device_tree);
-        if (device_service.dropped > 0) {
+        devices_broker.init(&device_tree);
+        if (devices_broker.dropped > 0) {
             // Otherwise entirely silent: drivers would just never see that hardware.
-            log.print("danos: WARNING {d} device(s) dropped — table full\n", .{device_service.dropped});
+            log.print("danos: WARNING {d} device(s) dropped — table full\n", .{devices_broker.dropped});
         }
 
         // Install the device-IRQ trampolines, so a driver's irq_bind has vectors to
@@ -285,10 +285,10 @@ fn kmain(boot_information: *const BootInformation) noreturn {
         status("no /sbin/init on the boot volume.\n");
     }
 
-    // Spawn the extra user binaries the loader ferried in the initrd (the VFS
+    // Spawn the extra user binaries the loader ferried in the initial_ramdisk (the VFS
     // server, and later device drivers). For now the kernel launches them all;
     // once init is a real service supervisor it will spawn them itself (system_spawn).
-    startInitrdBinaries(boot_information);
+    startInitialRamdiskBinaries(boot_information);
 
     // Become the idle task: drop below every real task and halt until an
     // interrupt. The timer keeps preempting into init and any other work.
@@ -297,22 +297,22 @@ fn kmain(boot_information: *const BootInformation) noreturn {
     architecture.halt();
 }
 
-/// Spawn every program bundled in the initrd as its own ring-3 process. A bad
+/// Spawn every program bundled in the initial_ramdisk as its own ring-3 process. A bad
 /// image or a program that fails to load is logged and skipped — the rest of the
 /// system still runs.
-fn startInitrdBinaries(boot_information: *const danos.BootInformation) void {
-    if (boot_information.initrd_len == 0) return;
-    const image = @as([*]const u8, @ptrFromInt(danos.physicalToVirtual(boot_information.initrd_base)))[0..boot_information.initrd_len];
-    const rd = initrd.Reader.init(image) orelse {
-        status("initrd: bad image, skipping\n");
+fn startInitialRamdiskBinaries(boot_information: *const danos.BootInformation) void {
+    if (boot_information.initial_ramdisk_len == 0) return;
+    const image = @as([*]const u8, @ptrFromInt(danos.physicalToVirtual(boot_information.initial_ramdisk_base)))[0..boot_information.initial_ramdisk_len];
+    const rd = initial_ramdisk.Reader.init(image) orelse {
+        status("initial_ramdisk: bad image, skipping\n");
         return;
     };
     var i: u32 = 0;
     while (i < rd.count) : (i += 1) {
         const item = rd.entry(i) orelse continue;
-        statusPrint("starting /sbin/{s} (from initrd)...\n", .{item.name});
+        statusPrint("starting /sbin/{s} (from initial_ramdisk)...\n", .{item.name});
         process.spawnProcess(item.blob, 4) catch |err| {
-            statusPrint("initrd: {s} failed to load: {s}\n", .{ item.name, @errorName(err) });
+            statusPrint("initial_ramdisk: {s} failed to load: {s}\n", .{ item.name, @errorName(err) });
         };
     }
 }