feat(bitable): U5 R4 grouping (max 3 fields) + conditional formatting (7 operators)
- GroupingEditor: multi-select field picker (max 3), per-level direction
toggle, reorder buttons, "已知限制：不支持跨分组多选" note, empty state
- ConditionalFormatEditor: per-rule enable/field/operator/value/color/bold,
8 color keys, WCAG 1.4.1 bold default true, first-match-wins footer legend
- BitableGrid: unified section rendering (grouped/ungrouped via single
vxe-grid declaration), group headers as separate divs (CF only on data
cells), CF via row-config.className, multi-grid instance map for refresh
- groupingRulesUtils: pure functions for CF matching (7 operators), group
tree builder, SUM/AVG aggregation, CSS var mappers, self-check on load
- view_config.py: Pydantic v2 validation (MAX_GROUP_BY_FIELDS=3, 7
operators, 8 color keys, extra="forbid" on sub-models)
- routes/bitable.py: validate_view_config on PATCH (HTTP 422 on error)
- stores/bitable.ts: updateViewConfig action (merges U5 sub-keys, preserves
filters/sort/hidden_fields)
- ViewConfigPanel: grouping + conditional-format tabs
- E2E: 8 scenarios (G1-G8: single/multi grouping, collapse/expand, CF
equals/between, combined, aggregation)
- Tests: 54 unit tests (19 grouping + 35 CF), 2 PG-marked skipped
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