docs: lock scope to lô tô hội chợ tân tân variant

- pdr: explicit in-scope (9x9, 5/row + 5/col, ascending cols, single-row
  Kinh, "Chờ N", continue-after-win) vs out-of-scope (3x9 european
  bingo 90, two-line / full-house tiers, custom number ranges)
- update codebase-summary, system-architecture, development-roadmap to
  reflect 11x9 master board, draw-order overlay, exact 5/col picker
- add researcher report comparing tân tân vs european bingo 90

web/docs/project-overview-pdr.md

@@ -2,15 +2,50 @@
 
 ## What is Lô Tô?
 
-Lô tô is a traditional Vietnamese bingo game. The app replicates the game digitally for players to generate their own 9×9 number cards and mark cells as a host calls numbers from 1–90. First player to complete an entire row wins and shouts "Kinh!" (the game's victory cheer).
+This app replicates **Lô tô hội chợ** (Vietnamese fairground / carnival lô tô),
+specifically the **Tân Tân** style most familiar from southern Vietnam class
+reunions and Tết gatherings. Inspiration: TN1 class reunions (2014–2017)
+where players ran build of physical bingo cards.
 
-The inspiration comes from TN1 class reunions (2014–2017) where players often ran build of physical bingo cards.
+It is **not** the British Bingo 90 / Italian Tombola 3×9 / 15-number ticket.
+That format is intentionally out of scope.
+
+## Game Variant & Scope
+
+### In scope (Lô tô hội chợ Tân Tân)
+- **Card**: 9 rows × 9 columns. Exactly **5 numbers per row** AND exactly
+  **5 numbers per column** (45 numbers per card; 36 blanks).
+- **Column ranges**: col 0 = 1–9, col 1 = 10–19, …, col 7 = 70–79,
+  col 8 = 80–90.
+- **Within a column**: numbers placed top-to-bottom in **ascending** order.
+- **Number pool**: 1–90.
+- **Win condition**: 1 row complete = **"Kinh!"**. After winning, the player
+  may keep playing further rows (game does not end).
+- **Waiting state**: when a row needs only 1 number, app announces **"Chờ N"**.
+- **Host (quản trò)** draws numbers from a shuffled 1–90 deck, tracks them on
+  a master board, and may also play their own card.
+
+### Out of scope
+- 3×9 / 15-number Bingo 90 / Tombola tickets (European format).
+- Two-line and full-house win tiers.
+- Custom number ranges (1–75 American bingo, etc.).
+- Stake / pot / payout logic.
+- Multiplayer real-time sync.
 
 ## Core Mechanics
 
-- **Players**: Generate a randomized 9×9 card with 45 numbers (5 per row, weighted distribution across columns 1–90). Click cells to mark them as numbers are called.
-- **Host**: Draws numbers randomly from a shuffled 1–90 deck, displays the current number on a large board, and tracks which numbers have been called.
-- **Bingo**: When a row is complete, the player's card triggers a celebration popup showing "Kinh!" with confetti emojis. Before bingo, toast notifications prompt "Chờ X" (waiting for X) when only one number remains in a row.
+- **Players**: Generate a randomized 9×9 card. The generator guarantees 5 per
+  row and 5 per column (constraint-aware picker, not loose weighted random).
+  Numbers within each column ascend top-to-bottom. Click cells to mark them.
+- **Host**: Draws numbers randomly from a shuffled 1–90 deck, shows the
+  current number, and tracks all called numbers on an **11×9 master board
+  aligned by ones-digit** (col 0 = 1–9, col 8 = 80–90; 1 / 11 / 21 / … / 81
+  share row 1, etc.). Each called cell shows its 1-based **draw order** as a
+  small superscript so the host can quickly verify a "Kinh!" claim by reading
+  the order across the winning row.
+- **Bingo**: When a row is complete, a celebration popup shows "Kinh!" with
+  confetti. Player keeps playing afterward — no game-end gate.
+- **Waiting**: "Chờ N" toast when a row is one number away.
 
 ## Tech Stack
 
@@ -37,11 +72,14 @@ State is entirely client-side. Each page/card instance uses a unique localStorag
 
 ## Key Acceptance Criteria
 
-- [x] Player can generate a new 9×9 card with valid number distribution.
+- [x] Player card is 9×9 with **exactly 5 per row and 5 per column**.
+- [x] Numbers within each column are **ascending top-to-bottom**.
 - [x] Player can click cells to toggle crossed state.
 - [x] Bingo popup triggers when row is complete, shows row number and "Kinh!" message.
+- [x] Player may keep marking after a Kinh — no game-end lock.
 - [x] Toast notifications show "Chờ X" before bingo (one number remaining).
-- [x] Host can draw numbers and see them on the 9×10 master board.
+- [x] Host can draw numbers and see them on the **11×9 last-digit-aligned master board**.
+- [x] Master board shows **draw order** on each called cell for Kinh verification.
 - [x] Host has their own player card (isolated by localStorage prefix).
 - [x] Offline persistence via localStorage (grid and crossed state).
 - [x] Dark mode support (Tailwind dark classes).
@@ -65,4 +103,4 @@ State is entirely client-side. Each page/card instance uses a unique localStorag
 - Multiplayer sync (real-time via WebSocket)
 - i18n beyond Vietnamese
 
-Last reviewed: 2026-04-26
+Last reviewed: 2026-04-26 (scope locked: Lô tô hội chợ Tân Tân)