feat: UI polish v2 + installable PWA with offline audio

Phase 1 — Vietnamese-safe font + master empty state:
- Add @fontsource/roboto-condensed (700 weight, all subsets including
  Vietnamese). font-display:swap. tan-tan-num now resolves the bundled
  face on Android instead of system Arial Narrow.
- New MasterEmptyState.svelte: ghost 11×9 grid + "Chế độ Quản trò"
  pill + readiness microcopy. Replaces the bare line of text in
  MasterPanel's no-game state.

Phase 2 — Mode picker icons, color picker layout, header polish:
- Inline SVG glyphs above each mode button (player card / megaphone /
  two stacked cards). Communicates role at a glance.
- Color picker wrapped in a single bordered card with "Tuỳ chỉnh"
  and "Mẫu sẵn" sub-headers.
- "Mặc định" → "Đặt lại" with a bordered chip style — clearer
  affordance than the previous near-invisible footer link.
- Header subline: drop tracking-[0.28em] all-caps SaaS look; replace
  with dash-flanked lantern band ("— 🏮 Hội chợ TN1 —") for
  fairground mood.

Phase 3 — Installable PWA + offline audio:
- @vite-pwa/sveltekit with autoUpdate. Precache app shell (~353 KB
  → 213 entries) PLUS the default voice's 92 clips so first-install
  is fully offline-capable. Alternate voices fall through to a
  CacheFirst runtime rule (cached on first play, 30-day TTL,
  maxEntries: 400 for future-proofing).
- New static/manifest.webmanifest (Lô tô — Hội chợ TN1, theme #1565c0,
  background #0a0f1f, standalone, vi).
- Icons: 192/512 standard + 512 maskable, generated from a single
  rose-amber-gradient SVG source.
- app.html: manifest link, dual theme-color meta (light + dark),
  apple-touch-icon, apple-mobile-web-app-capable for proper
  standalone launch on iOS Safari.
- _headers: add manifest-src + worker-src to CSP; no-cache on /sw.js
  and /manifest.webmanifest so deploys propagate.

Tests: 115/115 pass. Build clean (305 precache entries, 0 glob
warnings).

Reviewer concerns (addressed):
- maxEntries bumped 200 → 400 (was barely enough for 2 voices).
- Default voice precached so offline-first promise holds without
  requiring users to play every clip online first.
- "do NOT add skipWaiting" comment added next to autoUpdate.

web/docs/development-roadmap.md

@@ -12,15 +12,19 @@ now", see `docs/project-overview-pdr.md` and `docs/codebase-summary.md`.
 - "Quản trò đọc số" voice now speaks Chờ/Kinh on master in "both" mode
 - One-shot migration: `masterMode: true` → `mode: "both"`
 
+### UI Polish v2 + Installable PWA (2026-04-27)
+- **Font**: Roboto Condensed self-hosted via @fontsource (Latin + Vietnamese subsets), swapped into `tan-tan-num` stack
+- **Empty State**: New `MasterEmptyState.svelte` component for first-run host (mirrors player UX)
+- **Mode Picker**: 3-way segmented toggle with inline SVG glyphs (player/master/both)
+- **Color Picker**: Bordered card with "Mẫu" (presets) + "Tuỳ chỉnh" (custom input) sections
+- **Header Polish**: Decorative dashes flanking subline (replaced all-caps tracking)
+- **PWA**: @vite-pwa/sveltekit generates SW + manifest. App shell precache (~353 KB). Audio runtime caching (CacheFirst). Auto-update w/ reload toast. Works offline at fairground (no signal venues)
+
 ## Idea Phase
 
 ### Undo Last Cell
 Allow player to undo the most recent cross/uncross action. Requires change history or state snapshot. **Status**: Idea (low priority)
 
-
-### PWA Install
-Add service worker and manifest for "Install App" prompt on Android/iOS. **Status**: Idea (would require server-side components)
-
 ## Considered Phase
 
 ### Multiplayer Sync (Real-time)
@@ -86,4 +90,4 @@ All decisions follow **YAGNI** (You Aren't Gonna Need It), **KISS** (Keep It Sim
 Future work gates on **real user demand**, not speculation.
 
 Last reviewed: 2026-04-27
-Last synced: 2026-04-27 (6-phase refactor)
+Last synced: 2026-04-27 (UI polish v2 + PWA shipped)