Add Bopomofo (注音) keyboard layout

[AshBuk]

Add Traditional Chinese Bopomofo (Zhuyin / 注音) layout — the standard phonetic input layout used in Taiwan, mapped onto a QWERTY base.

Scope note: This is a phonetic layout where each key is mapped to a Bopomofo symbol (ㄅ ㄆ ㄇ ㄈ ...). Pinyin-based input methods (which require an IME composition layer) are out of scope for this issue — open a separate discussion if interested.

File to create: gui/src/js/layouts/zh-bopomofo.js

Reference layouts:

• gui/src/js/layouts/en-qwerty.js — physical key positions
• gui/src/js/layouts/ru-jcuken.js — closest analogue (non-Latin script mapped to QWERTY positions)

Each layout file exports a window.LAYOUT_XX_YYYY object with: id, name, language, rows, fingerMap, leftHandKeys, shiftToBaseKey. Keep the field order and code style consistent with the reference files.

Steps:

1. Create gui/src/js/layouts/zh-bopomofo.js
2. Register in gui/src/js/layouts.js (autoRegister)
3. Add <script> tag in gui/index.html
4. Apache-2.0 license header at the top

Acceptance checklist:

• Layout renders all Bopomofo symbols correctly
• Finger mapping verified against the standard Bopomofo physical layout
• Tone marks (ˊ ˇ ˋ ˙) on correct positions
• make lint, make test, wails build all pass
• Verified by a native Bopomofo typist from Taiwan

Dev setup and CI requirements: see docs/CONTRIBUTING.md.

Requires familiarity with Bopomofo input.