[smithbr]

Makes CI green and aims for a warm-cache wall-clock time under 1:30.

Fixes

• scripts/link.sh: on macOS /bin/bash 3.2 under load, printf could fail with EINTR when a child exited, which dropped a list line. This was why link.bats "a second run changes nothing" failed on main: run 1 lost an editor link and run 2 made it. The lists are now collected before they are printed.
• scripts/doctor.sh: reads link.sh's output through a temp file, for the same EINTR reason.
• Tests no longer touch the real ~/.gitconfig or /opt/homebrew, and pass from a checkout under a symlinked path.

Speed (coverage unchanged: same @test count in every file)

• link.sh: fewer subshells and processes, output identical across 30 compared commands. link.bats uses about 40% less CPU.
• bin_scripts.bats is split into bin_scripts, bin_pihole, bin_ph_backup, and bin_firetv, with no real sleeps and mocks written once per file.
• deps, ai_doctor, doctor, install: fixtures built once, sleeps dropped.

CI: five macOS Bats shards (the account's concurrent macOS limit), balanced by measured time. The separate shellcheck job becomes a step in the lightest shard.