init: data-driven boot service list via /etc/init.csv

Replace init's hardcoded boot_services array with an authoritative,
human-readable service list read at boot, mirroring /etc/devices.csv. Each row
is a service binary path followed by its argv; startup order is file order,
shutdown the reverse. There is no hardcoded fallback — a missing file starts
nothing (the no-ramdisk isolation behavior).

- library/csv: shared CSV helpers (comment strip, field iteration) with unit
  tests; device-registry is refactored onto them so both /etc/*.csv files parse
  through one place.
- init reads /etc/init.csv into fixed-max static tables (the same pattern as the
  device registry) and passes each row's argv straight to spawnSupervised. This
  also makes boot-time modes (e.g. device-manager test-usb-restart) expressible
  as data rather than hardcoded.
- Diagnose mode (-Ddiagnose omits the display stack) becomes build-time file
  selection between etc/init.csv and etc/init-diagnose.csv, so init carries no
  comptime service logic; the diagnose build option is dropped from init.
- build.zig: csv module wired; /etc/init.csv bundled into the initrd; the
  device-registry tests move to a dedicated block since they now import csv.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KJqSiLLchDUUCoXn5jsiwd

etc/init-diagnose.csv

@@ -0,0 +1,12 @@
+# /etc/init.csv — diagnose variant (-Ddiagnose), bundled at /etc/init.csv.
+#
+# The display stack (display, display-demo) is omitted so the kernel's timestamped
+# on-screen boot transcript is never suppressed — the bring-up timeline (USB,
+# storage, logger) stays readable on real hardware with no serial. See etc/init.csv
+# for the format; this file must otherwise track it.
+#
+# service                          args...
+/system/services/input
+/system/services/device-manager
+/system/services/fat
+/system/services/logger