refactor: rewrite from Next.js + React to SvelteKit + Svelte 5

Full stack swap to enable future extension (more pages / load functions /
backend) while keeping JSDoc-only code style.

Stack:
- SvelteKit 2 + adapter-static
- Svelte 5 runes ($state, $derived, $effect, $props)
- Vite 7 + @sveltejs/vite-plugin-svelte 6
- Tailwind 4 (Vite plugin)
- ESLint 9 (flat) + eslint-plugin-svelte
- Pure JS + JSDoc, no TypeScript

Source moves:
- app/page.jsx              → src/routes/+page.svelte
- app/master/page.jsx       → src/routes/master/+page.svelte
- app/layout.jsx            → src/routes/+layout.svelte (+ +layout.js)
- components/player-board.jsx → src/lib/PlayerBoard.svelte
- lib/game-logic.js         → src/lib/game-logic.js (verbatim)
- next.config.mjs           → svelte.config.js + vite.config.js
- app/globals.css           → src/app.css
- (new)                     → src/app.html

Behavior preserved: PlayerBoard with bingo "Kinh!" popup + waiting "Chờ X"
toast, master 9x10 tracking board with shuffled draw, host's own player
card via storagePrefix="loto_master_card", localStorage prefix model
(loto_*, loto_master, loto_master_card_*), basePath dual mode (CF default
empty, BUILD_PROFILE=gh → /loto, codeserver dev → /absproxy/{port}).

A11y kept from prior hardening: role-correct buttons, aria-pressed on
cells, role=dialog modal with Escape, role=status toast.

Plans: ts-to-jsdoc plan marked completed; sveltekit-refactor plan tracks
the work above. Docs under ./docs/ rewritten by docs-manager subagent to
match the SvelteKit terminology.

web/docs/development-roadmap.md

@@ -39,7 +39,7 @@ Host and players connect via WebSocket to sync called numbers and state. Require
 - Remote tournaments
 - Master board auto-updates all players in real-time
 
-**Consideration**: Out of scope for static export. Requires major refactor (Next.js API routes + WebSocket server). Deferred indefinitely.
+**Consideration**: Out of scope for static export. Requires major refactor (SvelteKit API routes + WebSocket server). Deferred indefinitely.
 
 ### i18n Beyond Vietnamese
 Internationalization (English, Chinese, etc.). Requires extraction of all Vietnamese strings and i18n library (next-intl). **Status**: Considered (low demand for non-Vietnamese users)
@@ -53,17 +53,17 @@ Full undo/redo stack with history navigation. Adds complexity to state managemen
 - Game logic: `generateGrid()`, `isRowComplete()`, `getWaitingNumber()`
 - localStorage helpers: `saveGrid()`, `loadGrid()`, etc.
 
-**Tech**: Jest + @testing-library/react
+**Tech**: Vitest (Vite's native test runner)
 
 ### Component Tests
-- PlayerBoard with mocked localStorage
+- PlayerBoard with mocked localStorage, $state/$derived verification
 - Master page with different game states
 
 ### E2E Tests
 - Player flow: generate card → click cells → verify bingo popup
 - Host flow: new game → draw numbers → verify board state
 
-**Tech**: Playwright or Cypress
+**Tech**: Playwright
 
 ## Future Enhancements (Speculative)
 
@@ -88,11 +88,12 @@ Support 8×8 or 10×10 grids. Major refactor (NUM_ROWS, NUM_COLS constants, weig
 
 ## Decision Rationale
 
-All decisions follow **YAGNI** (You Aren't Gonna Need It):
-- No multiplayer sync → adds server dependency, breaks static export model
-- No i18n → Vietnamese-only community, localizing adds complexity without demand
-- No testing → small codebase, manual testing covers critical paths; add tests when code grows or bugs surface
-- No undo/redo → simple game, mistakes are part of play experience
+All decisions follow **YAGNI** (You Aren't Gonna Need It), **KISS** (Keep It Simple), **DRY** (Don't Repeat Yourself):
+- No multiplayer sync → adds server dependency, breaks static export (Cloudflare Pages)
+- No i18n → Vietnamese-only community, localizing adds complexity
+- No testing → small codebase (<300 LOC), manual testing covers critical paths; add when code grows
+- No undo/redo → simple game, mistakes are play experience
+- Svelte 5 runes → cleaner reactivity than hooks, smaller mental model
 
 Future work gates on **real user demand**, not speculation.