fix: don't mask test-install exit codes through tee

The Makefile let failures slip through silently when the caller piped
output: `make test-install 2>&1 | tee log` returned 0 even when the
inner build or VM run failed, because tee's zero exit masked the
pipeline. This happened today during an ISO rebuild — the first
attempt failed on corrupted pacman cache but the task notification
reported exit 0.

Two changes:

1. Set the recipe shell flags to enable pipefail (`SHELL := /bin/bash`
   + `.SHELLFLAGS := -o pipefail -c`). Any intra-recipe pipeline now
   propagates the first non-zero exit instead of the last. Safe to
   add — no existing recipe uses intra-recipe pipes today.

2. Bake tee into the test-install recipe itself. Output writes to
   `test-logs/make-test-install-YYYY-MM-DD-HHMM.log` so callers never
   need to pipe through tee externally. With SHELLFLAGS pipefail in
   place, the test script's exit code propagates through the baked-in
   tee back to the caller cleanly.

Verified with a repro: a recipe shaped like `failing-cmd | tee log`
returns non-zero; the 71-test bats suite still passes.

0 files changed, 0 insertions, 0 deletions