wip(build): acceptance boots a fresh data stick -- every run is a first boot (#92, Task 3) [skip ci]

Not yet accepted (plan 2026-10-29-stick-5, Task 3).
- kernel/Makefile: a v4 `qemu` boot attaches a fresh data stick
  (DATASTICK=1) and nothing else; ARTDISK/ZUSEDISK keep the minted pair only
  for system=v3 (QEMU_V3_BOOT, from KERNEL_ARGS).
- qemu_session.py: the Makefile's defaults for every mode but those that ask
  for the pair by name (stick_artemis, two_sticks, artemis_unsigned,
  raw_ident, v3_keys) or for no drive; `zuse` now expects the genesis line.
- nightly.sh: accept stick-high runs stick_genesis (the stick as built).
- .claude/CLAUDE.md "The disks", the stick-high line; disk/README.md (the
  pair: tests and v3 only); STICK.md 11, increments 3 and 5 done.

Before the change: zuse on amd64 FAIL -- the pair's "identity confirmed",
no genesis line (logs/20261108-130732).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2

docs/v4.0.0/STICK.md

@@ -352,6 +352,9 @@ first and seen to fail:
    `qemu` targets behind `DATASTICK=1`, off by default -- until increments 4 and 5 the kernel cannot
    take Artemis from it or mint Zuse onto it, so as the default it would leave every acceptance boot
    headless. Increment 5 turns it on and retires the scratch pair and the virtio disk.
+   **Done 2026-11-08** (plan `2026-10-29-stick-5`, Task 3): a v4 `qemu` boot attaches a fresh data
+   stick and nothing else; the scratch pair stays only for the tests that ask for it and for
+   `system=v3`.
 4. **Artemis and Zuse from one disk:** the boot device from the loader, the partitions found and
    attached, virtio Artemis off the v4 path; recognition of a minted stick; entropy on the v4 path;
    `system=v3` refused on a stick (§4, §5).
@@ -361,6 +364,8 @@ first and seen to fail:
    recorded) and a 4 GB one (below the minimum: not grown, said so).
    **Amended 2026-10-29:** the genesis is the proxy's, with the version 2 marker (§6); the fresh
    stick's first boot reaching `[zuse@Hera] ok>` with nothing set up is the test of plug and play.
+   **Done 2026-11-08** (plan `2026-10-29-stick-5`, Tasks 1-3; `FABRIC-3.md` XLVIII.8-9): growth is
+   capped at 256 GiB (R1); every acceptance run is now a first boot.
 5a. **The real Zuse stick (2026-10-29)** (§6a): `MINT-ZUSE` and its confirmation, the GPT and
    identity written to the second stick, the marker's real key; recognition of the real Zuse
    stick; the fixed screen and its R; the old stick refused after a replacement.