Feat: Alphanumeric Coordinate Grid on Alternate View (#2938)

## Description:

Adds a coordinate grid to the Alternate View (holding spacebar) using
numbers on the X-axis, and letters on the Y-axis. No more "he's
attacking you in that—well, the little peninsula thing... next to the
island! which island? uhh..." moments when playing with friends.
Optimally maps have letters A-J (just like in the Battleships board
game) but special maps like Amazon River dynamically resize to only have
2 letters so as to not have too many number columns. This feature
overall can be toggled via the settings menu.

Also saw it requested on the [official
discord](https://discord.com/channels/1359946986937258015/1457037351422263480)
a couple times, thought it was a neat idea.

### World Map
<img width="3809" height="1824" alt="image"
src="https://github.com/user-attachments/assets/dab56879-a34e-48ea-a588-2907d26feb45"
/>

### Scales correctly when zoomed in
<img width="3798" height="1874" alt="image"
src="https://github.com/user-attachments/assets/7e06a47f-d3d9-4f92-8e89-3eaf866e9b25"
/>

### Amazon River
<img width="3803" height="1595" alt="image"
src="https://github.com/user-attachments/assets/4797c576-20b2-4aa8-8b7a-107078ab6308"
/>

### Enable/Disable via settings


https://github.com/user-attachments/assets/ec9f4e07-70a1-4f9d-b137-c3c3d2a2540c

## 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:

bijx

---------

Co-authored-by: iamlewis <lewismmmm@gmail.com>

src/client/HelpModal.ts

@@ -42,6 +42,7 @@ export class HelpModal extends BaseModal {
     const isMac = /Mac/.test(navigator.userAgent);
     return {
       toggleView: "Space",
+      coordinateGrid: "KeyM",
       centerCamera: "KeyC",
       moveUp: "KeyW",
       moveDown: "KeyS",
@@ -265,6 +266,14 @@ export class HelpModal extends BaseModal {
                       ${translateText("help_modal.action_alt_view")}
                     </td>
                   </tr>
+                  <tr class="hover:bg-white/5 transition-colors">
+                    <td class="py-3 pl-4 border-b border-white/5">
+                      ${this.renderKey(keybinds.coordinateGrid)}
+                    </td>
+                    <td class="py-3 border-b border-white/5 text-white/70">
+                      ${translateText("help_modal.action_coordinate_grid")}
+                    </td>
+                  </tr>
                   <tr class="hover:bg-white/5 transition-colors">
                     <td class="py-3 pl-4 border-b border-white/5">
                       ${this.renderKey(keybinds.swapDirection)}