Gate `boot-pi5-serial`: the full Home kernel boots on a real Pi 5 to the interactive serial shell, scripted from the Mac (Phase 7b's first half)

Epic: #113 · Milestone: MC2 — Pi 5 bring-up

Why

This is the first hardware truth of the whole plan: the same milestone list CI asserts in QEMU, asserted on silicon, via the rig from #48. Until it is green, no display/audio/media issue can claim progress on hardware.

Tasks

• scripts/pi/boot-gate-pi5.sh: build.sh rpi5 --profile=serial → pi-deploy.sh (TFTP) → pi-power.sh cycle → capture serial 90 s → assert scripts/boot-milestones-aarch64.txt in order → feed scripts/boot-commands.txt (echo, ls, cat, ps, uname, irq, dtb) and assert outputs → exit code.
• uname reports HomeOS aarch64 rpi5; irq shows timer + UART RX counts increasing after the script types a character.
• Failure artefacts: full serial log, bootloader log, image checksum, firmware/EEPROM version.
• Record the first passing run (log + photo) in docs/testing/PI5_E2E.md and flip the Phase 7b row in IMPLEMENTATION_STATUS.md to "serial boot: PASS (hardware, date)".

Acceptance

Script exits 0 three runs in a row on the rig; MASTER_PLAN Phase 7b "serial boot" half marked done with the measured boot time.

Size: S (once the deps land) · Depends on: #57, #58, #61, #54 · Blocks: MC3, MC4