Make zig-out a FHS image, and the boot volume

`zig build` now installs into a FHS-shaped zig-out that *is* the danos filesystem
and the boot volume — no more zig-out/bin or a separate esp/:

  zig-out/EFI/BOOT/BOOTX64.efi        (firmware entry; UEFI fixes this path)
  zig-out/boot/initial-ramdisk.img
  zig-out/system/kernel               (the kernel binary)
  zig-out/system/services/init  vfs
  zig-out/system/drivers/hpet   bus

Binaries land at their addressed, leaf-collapsed paths per the sub-project
resolution rule (system/services/init/init.zig -> system/services/init); vfs, hpet,
and bus are installed to their FHS homes too, so the image is complete even though
at boot they arrive inside the initial-ramdisk.

The bootloader (boot/efi.zig) now loads each artifact from its FHS path
(system\kernel, system\services\init, boot\initial-ramdisk.img); run-x86-64 mounts
zig-out directly; the QEMU test harness assembles its ESP from the FHS zig-out.

Also renames system/kernel/main.zig -> kernel.zig so the kernel follows the
name/name.zig convention (kernel/ = ring-0 code, services/ = ring-3 OS services).
Documents the resolution rule in the repository-layout section (README + coding
standard). Suite 35/35 plus host tests green.

docs/coding-standards.md

@@ -137,6 +137,11 @@ single word or acronym needs no hyphen: `scheduler.zig`, `paging.zig`, `apic.zig
 `idt.zig`. (The module *alias* a file is imported under still follows the code
 conventions above — `snake_case` — because it's an identifier, not a filename.)
 
+**A sub-project's entry point repeats its directory's name** — `init/init.zig`,
+`runtime/runtime.zig`, `hpet/hpet.zig` — and the sub-project is addressed by the
+*directory* (`system/services/init`, `library/runtime`), with the repeated leaf
+resolving away. See the repository-layout section of [README.md](README.md).
+
 ## Why acronyms are the line
 
 Because an acronym has no letters to restore. `MMIO` doesn't become "memory mapped