Feature Add retaliate keybind (#3801)

If this PR fixes an issue, link it below. If not, delete these two
lines.
Resolves #3174 

## Description:

This PR implements a keybind for retaliation against incoming non-bot
attacks (Players and Nations). It currently will target the most recent
(last in array) incoming attack when the keybind is pressed, choosing
the minimum of attack ratio or incoming attack troop size to retaliate
with. This correlates with the last displayed incoming attack on the
bottom modal. It works when there are multiple attacks (press multiple
times to retaliate against each consecutive attack). If the retaliation
size is smaller than the attack, the keybind can be pressed multiple
times to repeatedly blunt the incoming troop count.

Due to the current keybind logic KeyR cannot be used but Shift+KeyR can
so it is set to that until refactor.

<img width="867" height="121" alt="image"
src="https://github.com/user-attachments/assets/56e80810-4900-4db0-8ce7-1856e13529e5"
/>

No tests have been added as the retaliation feature doesn't seem to have
any to begin with since it is just an attack intent. The keybind is not
configured any differently than others. I did run all current tests and
was all good.

## 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:

n1ghtingal3

src/client/UserSettingModal.ts

@@ -647,6 +647,16 @@ export class UserSettingModal extends BaseModal {
         @change=${this.handleKeybindChange}
       ></setting-keybind>
 
+      <setting-keybind
+        action="retaliateAttack"
+        label=${translateText("user_setting.retaliate_attack")}
+        description=${translateText("user_setting.retaliate_attack_desc")}
+        defaultKey="Shift+KeyR"
+        .value=${this.getKeyValue("retaliateAttack")}
+        .display=${this.getKeyChar("retaliateAttack")}
+        @change=${this.handleKeybindChange}
+      ></setting-keybind>
+
       <setting-keybind
         action="swapDirection"
         label=${translateText("user_setting.swap_direction")}