App.tsx dropped from 2,729 to 1,636 lines through the module-breakup refactor
(U1-U7), now well under the 2,000-line cap. Remove its grandfathered entry
from scripts/line-count-baseline.json so the file is subject to the cap going
forward and can never regress above 2,000. Scoped change: only the App.tsx
entry is removed; every other ceiling is untouched (a full `--update` would
have re-derived the whole baseline and re-raised ceilings for unrelated
grown files, which AGENTS.md forbids).
U8 (App.tsx module-breakup plan).
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