test(bastion): cover the rescue boot path and record what it exposed

`provision debug` is the lab's recovery tool of last resort and had no
integration coverage on any architecture. Adding it -- x86_64 on KVM so
it runs in ~15 minutes, plus the aarch64 equivalent -- showed the rescue
environment coming up correctly but nothing ever listening on port 22.

Reproduced on both architectures, so it is neither ARM-specific nor an
emulation artefact, and it is orthogonal to the multi-arch work: x86_64
is unchanged by that. Documented in ARCHITECTURE.md with the leads worth
checking, rather than left as a silent gap.

Also restructures the ARM rescue suite to seed the machine into state
instead of discovering it first. That mirrors the DGX Spark situation --
SSH-onboarded, never PXE-discovered, architecture known only from its
record -- and holds the test to one emulated boot, since each spends
~15 of its ~18 minutes fetching Anaconda's stage2 under TCG.

KEEP_VM=1 leaves the VM up on failure; half-hour emulated runs are too
expensive to pay twice just to see what happened.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015nRFZXpKwUVE4SRSHw6GjF

bastion/package.json

@@ -23,6 +23,8 @@
     "test:integration:iso:host": "sudo -E $(which npx) vitest run -c tests/integration/vitest.config.ts -t 'ISO boot'",
     "test:integration:arm-iso": "vitest run -c tests/integration/vitest.config.ts -t 'ARM ISO'",
     "test:integration:arm-iso:host": "sudo -E $(which npx) vitest run -c tests/integration/vitest.config.ts -t 'ARM ISO'",
+    "test:integration:rescue": "vitest run -c tests/integration/vitest.config.ts -t 'x86 rescue boot'",
+    "test:integration:rescue:host": "sudo -E $(which npx) vitest run -c tests/integration/vitest.config.ts -t 'x86 rescue boot'",
     "test:integration:arm-pxe": "vitest run -c tests/integration/vitest.config.ts -t 'ARM PXE rescue'",
     "test:integration:arm-pxe:host": "sudo -E $(which npx) vitest run -c tests/integration/vitest.config.ts -t 'ARM PXE rescue'",
     "test:integration:arm-pxe-full": "ARM_PXE_FULL=1 vitest run -c tests/integration/vitest.config.ts -t 'ARM PXE'",