Configurable immunity timer (#2763)

## Description:

Resolve discussions about stalled PR
https://github.com/openfrontio/OpenFrontIO/pull/2460

<img width="724" height="348" alt="image"
src="https://github.com/user-attachments/assets/c2c9fa79-cace-431a-9ca4-b3656612fa9d"
/>

Changes:
- Added a `Player::canAttackPlayer(other)` function to determine whether
a player can be attacked.
- This function is now used in most places where a fight can occur:
    - AttackExecution (land attacks)
    - Naval invasion
    - Warship fight
- Nukes can't be thrown during the truce
- Immunity only affect human players. Nations and bot will fight as
usual, and can be fought against.
- The immunity timer uses minutes in the modal window.

UI:

- The immunity phase is displayed with a timer bar at the top. This is
from the original PR, to be discussed if it's not deemed visible enough:

<img width="632" height="215" alt="image"
src="https://github.com/user-attachments/assets/f5ab9aa0-bd4f-4503-b8d6-b40b121fba65"
/>


## 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:

IngloriousTom

---------

Co-authored-by: newyearnewphil <git@nynp.dev>

src/client/HostLobbyModal.ts

@@ -45,6 +45,8 @@ export class HostLobbyModal extends LitElement {
   @state() private gameMode: GameMode = GameMode.FFA;
   @state() private teamCount: TeamCountConfig = 2;
   @state() private bots: number = 400;
+  @state() private spawnImmunity: boolean = false;
+  @state() private spawnImmunityDurationMinutes: number | undefined = undefined;
   @state() private infiniteGold: boolean = false;
   @state() private donateGold: boolean = false;
   @state() private infiniteTroops: boolean = false;
@@ -514,7 +516,7 @@ export class HostLobbyModal extends LitElement {
                             id="end-timer-value"
                             min="0"
                             max="120"
-                            .value=${String(this.maxTimerValue ?? "")}
+                            .value=${String(this.maxTimerValue ?? 0)}
                             style="width: 60px; color: black; text-align: right; border-radius: 8px;"
                             @input=${this.handleMaxTimerValueChanges}
                             @keydown=${this.handleMaxTimerValueKeyDown}
@@ -524,6 +526,47 @@ export class HostLobbyModal extends LitElement {
                     ${translateText("host_modal.max_timer")}
                   </div>
                 </label>
+
+                <label
+                  for="spawn-immunity"
+                  class="option-card  ${this.spawnImmunity ? "selected" : ""}"
+                >
+                  <div class="checkbox-icon"></div>
+                  <input
+                    type="checkbox"
+                    id="spawn-immunity"
+                    @change=${(e: Event) => {
+                      const checked = (e.target as HTMLInputElement).checked;
+                      if (!checked) {
+                        this.spawnImmunityDurationMinutes = undefined;
+                      }
+                      this.spawnImmunity = checked;
+                      this.putGameConfig();
+                    }}
+                    .checked=${this.spawnImmunity}
+                  />
+                    ${
+                      this.spawnImmunity === false
+                        ? ""
+                        : html`<input
+                            type="number"
+                            id="spawn-immunity-duration"
+                            min="0"
+                            max="120"
+                            step="1"
+                            .value=${String(
+                              this.spawnImmunityDurationMinutes ?? 0,
+                            )}
+                            style="width: 60px; color: black; text-align: right; border-radius: 8px;"
+                            @input=${this.handleSpawnImmunityDurationInput}
+                            @keydown=${this.handleSpawnImmunityDurationKeyDown}
+                          />`
+                    }
+                  <div class="option-card-title">
+                    <span>${translateText("host_modal.player_immunity_duration")}</span>
+                  </div>
+                </label>
+                
                 <hr style="width: 100%; border-top: 1px solid #444; margin: 16px 0;" />
 
                 <!-- Individual disables for structures/weapons -->
@@ -691,6 +734,23 @@ export class HostLobbyModal extends LitElement {
     this.putGameConfig();
   }
 
+  private handleSpawnImmunityDurationKeyDown(e: KeyboardEvent) {
+    if (["-", "+", "e", "E"].includes(e.key)) {
+      e.preventDefault();
+    }
+  }
+
+  private handleSpawnImmunityDurationInput(e: Event) {
+    const input = e.target as HTMLInputElement;
+    input.value = input.value.replace(/[eE+-]/g, "");
+    const value = parseInt(input.value, 10);
+    if (Number.isNaN(value) || value < 0 || value > 120) {
+      return;
+    }
+    this.spawnImmunityDurationMinutes = value;
+    this.putGameConfig();
+  }
+
   private handleRandomSpawnChange(e: Event) {
     this.randomSpawn = Boolean((e.target as HTMLInputElement).checked);
     this.putGameConfig();
@@ -757,6 +817,9 @@ export class HostLobbyModal extends LitElement {
   }
 
   private async putGameConfig() {
+    const spawnImmunityTicks = this.spawnImmunityDurationMinutes
+      ? this.spawnImmunityDurationMinutes * 60 * 10
+      : 0;
     this.dispatchEvent(
       new CustomEvent("update-game-config", {
         detail: {
@@ -775,6 +838,9 @@ export class HostLobbyModal extends LitElement {
             randomSpawn: this.randomSpawn,
             gameMode: this.gameMode,
             disabledUnits: this.disabledUnits,
+            spawnImmunityDuration: this.spawnImmunity
+              ? spawnImmunityTicks
+              : undefined,
             playerTeams: this.teamCount,
             ...(this.gameMode === GameMode.Team &&
             this.teamCount === HumansVsNations