Fix Ctrl+Click for Macs, and alphabetize gitignore (#2720)

Resolves #2719 
- [X] Ran `npm run format`
- [X] Ran `npm run lint:fix`
- [X] Ran `npm test`
- [X] Manually tested fixes

## Description:

### What problem(s) was I solving?

On Mac, `Ctrl+Click` is commonly used as a substitute for right-click to
open context menus. However, in OpenFront, `Ctrl+Click` was triggering
both the context menu, AND causing an attack.

This effectively prevented Mac users from being able to ally with
bots/nations, as trying to ally would cause you to attack them.

### What changes did I make?
- `Ctrl+Click` on Mac no longer triggers an attack, allowing players to
properly interact with the alliance system

### How I implemented it

1. Added an `isMac()` method to `InputHandler` which encapsulates the
"is mac" logic, and lets it be mocked during tests
2. In the `onPointerUp` handler, added a check: if on Mac and
`ControlLeft` is held, emit a `ContextMenuEvent`, and then return
(instead of continuing to also create a `MouseUpEvent`)
3. Extracted magic numbers for mouse button checks into descriptive
helper methods (`isMiddleMouseButton`, `isNonLeftMouseButton`) for
improved code clarity
4. Added clarifying comments throughout the pointer event handlers

Last, alphabetized the `.gitignore` file and organized it into "Folders"
and "Files" sections to make it easier to read.

### How to verify it

#### Manual Testing
- [X] On a Mac, hold `Ctrl` and left-click on another nation - verify
the context menu opens (not an attack)
- [X] On a Mac, right-click should still open the context menu as
expected
- [X] On Windows/Linux, `Ctrl+Click` continue to work as before
(modifier key for build menu if configured)
- [X] Regular left-click still triggers attacks/interactions as expected

#### Automated Testing
- [x] New unit test added: `Mac Ctrl+Click Context Menu` - verifies that
`Ctrl+Click` on Mac emits `ContextMenuEvent` instead of `MouseUpEvent`

### Description for the changelog

Fixed `Ctrl+Click` on Mac to properly open the context menu instead of
triggering an attack, restoring the ability for Mac users to form
alliances with other nations.

## 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

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

.gitignore

@@ -1,15 +1,21 @@
+# Folders
+.claude/
+.clinic/
+.idea/
 build/
+coverage/
 node_modules/
 out/
-static/
-coverage/
-TODO.txt
-resources/images/.DS_Store
-resources/.DS_Store
-.env*
-.DS_Store
-.clinic/
-CLAUDE.md
-.idea/
+
 # this is autogenerated by script
 src/assets/
+
+static/
+
+# Files
+.DS_Store
+.env*
+CLAUDE.md
+resources/images/.DS_Store
+resources/.DS_Store
+TODO.txt