Add text size and keyboard settings (#38)

Settings sets the text size (100, 125 or 150 %) and the key of each
button, kept in this browser's storage and validated on load. Every font
size scales with --text-scale, and the dialogue box scrolls instead of
growing past the screen. The game screen's label, the Play message and
Help's control list name the current keys.

Screen reader announcements for every native screen and touch control
remapping remain.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PLAN.md

@@ -235,6 +235,13 @@ The numbered sections below keep their full scope. Each one opens with a checkli
 - "Open in this port" lists the landmarks with at least one map in `NATIVE_MAPS`, so the atlas never suggests travel through unported areas.
 - `tests/atlas.test.ts` compares every landmark position with `data/maps/landmarks.asm` and the flypoints with `data/maps/flypoints.asm`.
 
+## Implemented: interface settings
+
+- Settings, beside Help, sets the text size (Standard, Large, Largest: 100, 125 and 150 %) and the keyboard key of each button. Every font size in the stylesheet scales with `--text-scale`; the dialogue box scrolls instead of growing past the screen.
+- Change waits for the next key. Escape cancels, and Tab, Escape and Space stay reserved for focus, dialogs and scrolling. A key given to a new button leaves its old one, which then has no key until the player chooses one. Reset controls restores X, Z, Enter, Shift and the arrows.
+- The preferences live in this browser's `localStorage` (`crystal-preferences-v1`), validated on load; without storage the defaults apply. They are not game state, so saves and backups do not carry them. The reference player keeps the default keys.
+- The game screen's label, the Play message and Help's control list name the current keys.
+
 ## Implemented: the options
 
 - OPTION in the start menu runs `_Option` and returns to the start menu. The labels come from `StringOptions` and the settings from each routine's strings. Up and down move the ▶ with `OptionsControl`'s wrapping, left and right change the option under it, A on CANCEL, B or Start leaves. Each routine is ported from its bit handling: text speed cycles FAST, MID and SLOW through `GetTextSpeed` (`.Save` keeps only the high nybble), the battle scene, battle style, sound and menu account toggle with either direction, printing cycles through the five `GBPRINTER_*` levels through `GetPrinterSetting`, and the frame wraps through `TYPE 1` to `8`.
@@ -468,7 +475,8 @@ Acceptance: main-game/postgame playthroughs, representative optional content, ba
 - [x] Trainer card: both pages, with the ROM's card picture, leader faces and animated badges
 - [x] Options screen, with the battle style and menu account in effect
 - [x] Pokédex screen: New mode list and entries
-- [ ] Scalable text, configurable controls and fuller accessibility
+- [x] Scalable text and configurable keyboard controls
+- [ ] Fuller accessibility: announcements for every native screen and touch control remapping
 - [ ] Save slots with migration, atomic writes and import previews
 - [ ] Installable web app with offline app shell, safe updates and quota handling
 - [ ] Acceptance on physical iPhone and Android devices