Renders the trends-by-category table from the #264 id-keyed tree as an indented
parent/child hierarchy (parity with ComparePeriodTable): top-level parents carry
a chevron and fold their subtree down to a subtotal, with an "expand all /
collapse all" button. Collapsed by default; expansion state is persisted under a
trends-specific localStorage key (reports-trends-expanded), distinct from the
comparable tables. The "result before transfers" line is interleaved before the
transfers section instead of sitting at the bottom.
Collapse is purely visual: section subtotals, before/net results and totals come
from computeOverTimeResults over the raw tree, never the visible rows.
New pure module overTimeTableModel.ts (section grouping + collapse accessors)
keeps the component thin and unit-testable without a React render harness;
overTimeResults.ts is left untouched. 8 new tests; build + 728 vitest green.
Resolves#265
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
