feat(run): WS5 early exit and incomplete runs

[jdpigeon]

Implements docs/superpowers/plans/2026-09-23-ws5-early-exit-incomplete-runs.md (spec §1.2, §1.5, §11 WS5).

What changes

• End experiment early and a 1 s Escape hold end the run with no confirm. A tap of Escape does nothing. Escape no longer ends lab.js studies.
• The runtimes report onAbort(csv), separate from onFinish(csv), with the trials recorded so far.
• The run lifecycle lives in the store: EndRun (RunBar or escapeHoldEpic) sets isEnding, the reducer keeps the first Stop as runOutcome, and endRunFallbackEpic ends a run no runtime reported. The result screen and RunBar say "EEG" only when a headset was connected (selectRecordsEEG).
• The stop epic closes the EEG stream, saves behavior, then renames an ended-early run to *.incomplete.csv (new fs:markRecordingIncomplete). Clean, Analyze and the badges skip it; recordingExists still counts it, so the session number isn't reused.
• RunResult (feat(design): WS5 participant screens + run outcome Storybook states #273) shows "Saving…", then the complete result or "Experiment ended early". The RunBar shows the Escape-held hint. The run screen fits under the RunBar.

Fixes beyond the plan

• lab.js 23: a root end() doesn't stop the study. Aborts now use controller.jump('abort'), and the data is reported at once.
• jsPsych keeps waiting out post_trial_gap after an abort, so its data is reported at once too.
• A late report from an earlier run can't settle the next one.
• A failed behavior save no longer skips marking the run incomplete.

Verification

• typecheck, lint (0 errors), npm test (285/285), electron-smoke PASS.
• Electron playtest (Fixture): End early and hold-Escape write *.incomplete.csv (behavior rows, and a complete last raw row). A tap of Escape doesn't end the run. Clean doesn't list incomplete runs. The earlier incomplete session is left byte-identical. Preview writes nothing.
• Not run live, because they need native dialogs or file pickers: a full complete run, the session-taken prompt, ending an imported jsPsych study early, and behavior-only runs. Tracked as QA in TODOS.md.