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).

test/qemu_test.py

@@ -57,9 +57,9 @@ ARCHES = {
         ],
         "efi_app": ("EFI/BOOT/BOOTX64.efi", "BOOTX64.efi"),  # (dest in ESP, name in zig-out/bin)
         "kernel": ("kernel", "kernel"),
-        # Further files shipped on the ESP: the init user program and the initrd
+        # Further files shipped on the ESP: the init user program and the initial_ramdisk
         # (VFS server + drivers), both copied from zig-out/bin.
-        "extra": [("sbin/init", "init"), ("initrd.img", "initrd.img")],
+        "extra": [("sbin/init", "init"), ("initial-ramdisk.img", "initial-ramdisk.img")],
         # Built as a function so we can splice in per-run paths.
         "qemu_args": lambda a, esp, vars_fd, serial: [
             "-machine", "q35", "-m", "128M",
@@ -178,9 +178,9 @@ CASES = [
      "smp":    4,
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
-    # The initrd: the loader ferries a bundle of user binaries; the kernel parses
+    # The initial_ramdisk: the loader ferries a bundle of user binaries; the kernel parses
     # it and spawns each as a ring-3 process (here the VFS-server stub heartbeats).
-    {"name": "initrd",
+    {"name": "initial-ramdisk",
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # The user-space VFS: a client opens/writes/reads a file through the rt file
@@ -202,7 +202,7 @@ CASES = [
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # IRQ teardown: an exiting driver's line is masked and its slot cleared (so no
     # ISR notifies a freed endpoint), and a sibling owner sharing that endpoint
-    # keeps its own binding. The path hpetd never takes, since it runs forever.
+    # keeps its own binding. The path hpet never takes, since it runs forever.
     {"name": "irqfree",
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},