ALL-1871 PR-1: Editable cell component + error-guided UI in PreviewTable

## ALL-1871 PR-1 - Frontend: Editable cells + error UI in PreviewTable Linear: ALL-1871 ("In-line editing of CSV data in bulk upload preview") Branch: wilbo/all-1871-editable-preview-cells ### What to build Convert the read-only PreviewTable into an editable grid with error-guided UX. This is a PURE FRONTEND PR -- no backend changes, no re-validation calls yet (those come in PR-3). ### Key files CREATE: apps/dashboard/components/pages/ConnectPage/BulkUpload/EditableCell.tsx - Click-to-edit: renders a span normally; on click/focus switches to input - Modified cells: visually distinct (e.g. bg-amber-50 border-amber-400) - Error cells: red border + tooltip showing the validation error message - Tab key: moves focus to next editable cell in the row, then first cell of next row - Original value: accessible via tooltip on the modified indicator - Props: { value: string|null, originalValue: string|null, error?: string, onChange: (val: string) => void, fieldId: string, rowIndex: number } EDIT: apps/dashboard/components/pages/ConnectPage/BulkUpload/PreviewTable.tsx - Replace renderCell(row.fieldName) renderers with EditableCell for all editable fields (skip rowNumber) - Accept new props: editedCells: Record<number, Record<string, string>>, onCellEdit: (rowIndex: number, field: string, value: string) => void - Error list items in bottom panel: make each entry clickable -- on click, scroll to that row and focus the cell - Pass errorsByRow down to EditableCell for per-field error display EDIT: apps/dashboard/components/pages/ConnectPage/BulkUploadTab.tsx - Add const [editedCells, setEditedCells] = useState<Record<number, Record<string, string>>>({}) alongside previewData - Handler: handleCellEdit = (rowIndex, field, value) => setEditedCells(prev => ({ ...prev, [rowIndex]: { ...prev[rowIndex], [field]: value } })) - Reset editedCells in handleBackToUpload and handleUploadAnother - Pass editedCells and onCellEdit down to PreviewTable ValidationError shape (types.ts): { row: number; field: string; message: string; value?: unknown } Note: row is 1-indexed (matches rowNumber). errorsByRow map in PreviewTable already groups by row. ### Acceptance test - User sees preview table after uploading CSV with validation errors - Clicking a cell makes it editable (input appears) - Editing a cell marks it visually different from unedited cells - Hovering a modified cell shows tooltip with original CSV value - Cells with validation errors show red border and error tooltip - Clicking an error in the error list scrolls to and focuses that cell - Tab moves focus to next editable cell ### Does NOT include - Re-validation calls (PR-3) - Import sending edits to backend (PR-4) - Any backend changes ### Dependencies - None (first PR) ### Tests - Update PreviewTable.test.tsx: renders EditableCell, calls onCellEdit on change, error cell has red border class