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/services/vfs/vfs.zig

@@ -1,4 +1,4 @@
-//! /sbin/vfs — the user-space VFS server. Shipped in the initrd, spawned as a
+//! /sbin/vfs — the user-space VFS server. Shipped in the initial_ramdisk, spawned as a
 //! ring-3 process, and reached by every other process through IPC (the `runtime`
 //! file API marshals open/read/write/stat/close into calls to this server's
 //! endpoint, published under the well-known `vfs` service id).
@@ -101,10 +101,10 @@ fn handle(message: []const u8, out: []u8) usize {
             if (off + n > nd.size) nd.size = off + n;
             return writeReply(out, .{ .status = 0, .len = @intCast(n) }, &.{});
         },
-        .stat => {
+        .status => {
             const of = openAt(request.node) orelse return fail(out);
-            const st = protocol.Stat{ .size = nodes[of.node].size, .kind = 0 };
-            return writeReply(out, .{ .status = 0, .len = @sizeOf(protocol.Stat) }, std.mem.asBytes(&st));
+            const st = protocol.FileStatus{ .size = nodes[of.node].size, .kind = 0 };
+            return writeReply(out, .{ .status = 0, .len = @sizeOf(protocol.FileStatus) }, std.mem.asBytes(&st));
         },
         .close => {
             if (request.node < opens.len) opens[@intCast(request.node)].used = false;