Stage 7 polish: docs + mark Stage 7 done (Part H)

- new docs/UI_DESIGN.md (design system: shell, nav, tab-bar, tiles, board zoom/labels, HoldConfirm, banner rotator, result iconography)
- ARCHITECTURE: app-shell + announcement channel (mock->server) + hint place-on-board / no_hint_available contract + board-style setting
- FUNCTIONAL(+ru): hint-on-board, word-check constraints/throttle, board style
- PLAN: Stage 7 -> done + polish refinement note; CLAUDE sources list

docs/UI_DESIGN.md

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+# Scrabble Game — UI design system
+
+Visual and interaction conventions for the `ui` client. Behaviour lives in
+[`FUNCTIONAL.md`](FUNCTIONAL.md); cross-service architecture (including the global
+points this doc references) lives in [`ARCHITECTURE.md`](ARCHITECTURE.md). The client
+is **pure HTML5/CSS + Unicode** — no image/font/SVG assets; icons are CSS shapes or
+emoji glyphs. Tokens are CSS custom properties (`ui/src/app.css`), light/dark via
+`prefers-color-scheme` or an explicit Settings choice, and **Telegram-themeParams-ready**
+(the tokens can be overridden at runtime).
+
+## Layout shell (`components/Screen.svelte`)
+
+A mobile-app feel: the screen is a full-height flex column where the **nav bar grows**
+to absorb spare vertical space (its buttons stay top-aligned) and everything else —
+the announcement strip, the content, and the optional bottom tab bar — **pins to the
+bottom**, the strip directly above the content. Tall content scrolls within the content
+region. Every screen except Login uses `Screen`.
+
+## Navigation
+
+- **Back**: a thin, compact `<` drawn from two rotated CSS borders (`Header.svelte`
+  `.chev`) — lighter than a glyph.
+- **Hamburger**: a CSS three-bar (`Menu.svelte`), deliberately larger; opens a dropdown
+  of items (lobby: Profile/Settings/About; game: History/Chat/Check word/Drop game).
+- **Tab bar** (`TabBar.svelte`): square, borderless, evenly distributed buttons — a large
+  emoji icon over a tiny truncated label. A press highlights a rounded **square** behind
+  the icon (slightly larger than it) until release; spacing keeps adjacent labels from
+  touching. No text selection on nav / tab-bar / buttons (`user-select: none`).
+
+## Tiles & board
+
+- **Tiles**: the letter sits in the **top-left** corner (offset a touch more than the
+  value), the point value bottom-right; blanks show no value.
+- **Board zoom** (`Board.svelte`): a two-state zoom (full 15×15 ↔ ~9 cells) via
+  `transform: scale()` on an inner layer inside a **fixed-size viewport** (the page never
+  reflows; the viewport scrolls when zoomed), with a smooth transition. Cell/tile **text
+  lives in a counter-scaled layer** (`scale(1/z)`) sized in `cqw`, so labels stay a
+  constant size (relatively smaller at higher zoom). On touch, attempting to place a tile
+  auto-zooms in centred on the target; double-tap and pinch toggle.
+- **Bonus-square labels** — a Settings choice (`boardlabels.ts`): `beginner` shows a
+  split `3×` / `word` (localized слово/буква), `classic` a single `3W` / `3С`, `none`
+  nothing. Default **beginner**.
+- **Grid lines**: the inter-cell gap shows a contrasting `--cell-line` (darker in light,
+  lighter in dark) to avoid a wavy-line optical illusion.
+
+## Controls
+
+- **HoldConfirm** (`components/HoldConfirm.svelte`): the shared press-and-hold control. A
+  short tap opens a small popover above the button; a ~0.7 s hold runs the primary action
+  immediately. Reused by:
+  - **MakeMove** (appears when ≥1 tile is pending; the rack collapses its used slots and
+    shifts left to free room): a **🏁** button whose popover offers **Make move ✅** /
+    **Reset ❌**.
+  - **Game tab bar**: 🔄 Draw (disabled when the bag is empty), 🥺 Skip, 🛟 Hint (with a
+    remaining-count badge) — each confirmed by an **Ok ✅** popover; 🔀 Shuffle has no
+    label and no confirm. The under-board slot shows the **Scores: N** preview.
+
+## Announcement banner (`components/AdBanner.svelte`, `lib/banner.ts`)
+
+A one-line inset strip under the nav bar. Content is minimal markdown (text + links,
+escaped + linkified). A parameterised **rotator** drives messages: a fitting message
+holds `holdMs` (default 60 s) then cross-fades to the next; a message wider than the strip
+pauses (`edgePauseMs`), scrolls to its right edge at `scrollPxPerSec`, pauses, and repeats
+until the cycle exceeds `holdMs`. Today a **mock** provider rotates a long and a short
+message; the source becomes a server-driven channel later (see ARCHITECTURE).
+
+## Result / status iconography (`lib/result.ts`)
+
+Lobby rows show two lines (opponents, then result + score) with a large place-based emoji
+on the right: Victory 🏆 / Defeat 🥈 / Draw 🏅, and for 3–4-player games II 🥈 / III 🥉 /
+IV 🏅; active games show Your move 🟢 / Opponent's move ⏳; invitations use 💌.
+
+## Caveat
+
+Emoji are rendered by the platform's system emoji font, so their exact look varies across
+OSes — acceptable for the MVP, and consistent with the no-asset rule (no glyphs are
+downloaded).