Add fullscreen support: HUD button (desktop/Android) + iOS Add to Home Screen banner (#3688)

Resolves #3685

## Description:

Adds fullscreen support for both desktop and mobile:

**Desktop / Android** — a fullscreen toggle button in the in-game HUD
(right sidebar), next to the settings button. Icon switches between
expand/compress depending on current state, synced with
`fullscreenchange` event (works with F11 too). Hidden on browsers that
don't support `document.fullscreenEnabled`.

**iOS** — since Safari doesn't support the Fullscreen API, a dismissible
banner is shown on the main screen (above the lobby cards) explaining
how to add the game to the Home Screen for a fullscreen experience. The
banner includes:
- **How** button — opens a step-by-step guide modal with iOS version
detection (iOS 26+ shows updated steps for the new ··· menu location,
including the extra Share step inside the menu)
- **Later** — hides until next visit
- **Never** — permanently dismisses via localStorage
- **Click here** button styled as a speech bubble with a tail pointing
toward the Share button location (center for iOS ≤18, right for iOS 26+)

All user-facing strings are wired through `translateText()` with keys
added to `en.json`.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## UI changes: 
### For [Fullscreen API supported
browsers](https://caniuse.com/?search=fullscreen+api):


https://github.com/user-attachments/assets/026e6a67-d070-4a7e-897b-52396a43191e

### For safari on ios: (add to homescreen modal)

<img width="375" height="667" alt="IMG_2242"
src="https://github.com/user-attachments/assets/9d0a6454-8512-44cf-b6ed-989de3ff02bc"
/>
<img width="648" height="1292" alt="CleanShot 2026-04-22 at 11 29 27@2x"
src="https://github.com/user-attachments/assets/dba1c218-2b73-4bc0-ac7d-14962eb79327"
/>



## Please put your Discord username so you can be contacted if a bug or
regression is found:

fghjk_60845

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

.gitignore

@@ -10,6 +10,7 @@ resources/.DS_Store
 .DS_Store
 .clinic/
 CLAUDE.md
+NOTES.md
 .claude/
 .idea/
 # this is autogenerated by script