Add Hindi InScript keyboard layout

[AshBuk]

Add the Hindi InScript keyboard layout — the Indian government standard for Devanagari script input.

Scope note: InScript is a phonetic-style layout that uses dead keys for matras (vowel signs combined with consonants). The matra layer mapping is non-trivial and should be verified by a native Hindi typist. Other Indic scripts (Tamil, Bengali, Telugu, etc.) — open separate issues if needed.

File to create: gui/src/js/layouts/hi-inscript.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 on 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/hi-inscript.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:

• Consonant layer renders and maps fingers correctly
• Vowel / matra layer (Shift) verified against InScript spec
• Special characters (ं ँ ः ़ ्) on correct positions
• make lint, make test, wails build all pass
• Verified by a native Hindi/InScript typist

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

Requires familiarity with InScript and Devanagari.