shakedown: wave 14: guided picker for ./run (interactive, builds the run from answers)

[ugglr]

Asked for by the user: with no flags on a terminal, ./run now guides you instead of making you remember flags.

What it does

• interactive_picker(): bare ./run on a TTY detects the SKU for a header, then asks "verify a new Mac (thorough) vs quick check", and for the thorough path two follow-ups (strict gating, and the opt-in AI/LLM load). It echoes the command it built (-> ./run --store --strict), prints a one-line heads-up, and flows straight into the run.
• Sets the same variables the flags would, then the existing --store expansion and export STRICT pick them up (no reordering).
• The picker is the confirmation, so it sets SHAKEDOWN_YES=1 to skip the second "Proceed?" prompt.

Skipped cleanly (unchanged behavior)

Any explicit flag (ARGC > 0), a non-interactive stdin (-t 0 false: pipe / < /dev/null / CI), or SHAKEDOWN_YES=1 bypasses the picker entirely. Scripted and flag-driven use is identical to before.

Verification

• Picker logic (extracted function, piped answers): choice 1+y+n -> --store --strict; 1+n+y -> --store --llama; 2 -> default; 3 -> prints --help pointer and exits 0; all of 1/2 set SHAKEDOWN_YES=1 so the second prompt is skipped.
• PTY test (real terminal): the picker fires only on a TTY, shows the detected SKU + menu, and choice 3 exits 0 with no set -u error (the trap is installed ~300 lines later, after the picker).
• Non-interactive regression: ./run --no-sudo < /dev/null skips the picker (0 menu lines) and completes normally.
• Lint clean (shellcheck, bash -n, all PYEOF heredocs ast.parse, zero em dashes). Docs updated (README quickstart, Store Day Checklist now leads with ./run + "pick option 1", CHANGELOG).

Passed dad review: correctness clean (a flagged "will-break" trap-vs-set-u issue was a false positive, verified by ordering + the live PTY run); applied the consistency fixes (read -r -p, lowercase shakedown: header) and the simplicity fix (flow into the run instead of double-prompting).