feat(ocr-pipeline): generic cell-grid with optional vocab mapping

Extract build_cell_grid() as layout-agnostic foundation from
build_word_grid(). Step 5 now produces a generic cell grid (columns x
rows) and auto-detects whether vocab layout is present. Frontend
dynamically switches between vocab table (EN/DE/Example) and generic
cell table based on layout type.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin-lehrer/app/(admin)/ai/ocr-pipeline/types.ts

@@ -29,7 +29,7 @@ export interface SessionInfo {
   dewarp_result?: DewarpResult
   column_result?: ColumnResult
   row_result?: RowResult
-  word_result?: WordResult
+  word_result?: GridResult
 }
 
 export interface DeskewResult {
@@ -124,6 +124,49 @@ export interface WordBbox {
   h: number
 }
 
+export interface GridCell {
+  cell_id: string          // "R03_C1"
+  row_index: number
+  col_index: number
+  col_type: string
+  text: string
+  confidence: number
+  bbox_px: WordBbox
+  bbox_pct: WordBbox
+  ocr_engine?: string
+  status?: 'pending' | 'confirmed' | 'edited' | 'skipped'
+}
+
+export interface ColumnMeta {
+  index: number
+  type: string
+  x: number
+  width: number
+}
+
+export interface GridResult {
+  cells: GridCell[]
+  grid_shape: { rows: number; cols: number; total_cells: number }
+  columns_used: ColumnMeta[]
+  layout: 'vocab' | 'generic'
+  image_width: number
+  image_height: number
+  duration_seconds: number
+  ocr_engine?: string
+  vocab_entries?: WordEntry[]   // Only when layout='vocab'
+  entries?: WordEntry[]         // Backwards compat alias for vocab_entries
+  entry_count?: number
+  summary: {
+    total_cells: number
+    non_empty_cells: number
+    low_confidence: number
+    // Only when layout='vocab':
+    total_entries?: number
+    with_english?: number
+    with_german?: number
+  }
+}
+
 export interface WordEntry {
   row_index: number
   english: string
@@ -137,6 +180,7 @@ export interface WordEntry {
   status?: 'pending' | 'confirmed' | 'edited' | 'skipped'
 }
 
+/** @deprecated Use GridResult instead */
 export interface WordResult {
   entries: WordEntry[]
   entry_count: number