[small-fix 20 lines] Add FFA collusion warning

[a-happy-goose]

Resolves #3900

Description:

During the spawn phase in FFA games, display a collusion warning to clearly communicate to new users that pre-game agreement is not allowed.

• I have added screenshots for all UI updates
• I process any text displayed to the user through translateText() and I've added it to the en.json file
• I have added relevant tests to the test directory

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

goose126

[coderabbitai]

Walkthrough

This PR adds a heads-up warning message to inform new players that pre-game collusion is not permitted in FFA mode. The warning displays during spawn phase and includes a new English translation string defining the message content.

Changes

FFA Collusion Warning Feature

Layer / File(s)	Summary
FFA Collusion Warning in HUD src/client/hud/layers/HeadsUpMessage.ts, resources/lang/en.json	Import GameMode to check game mode, add conditional rendering in spawn phase for FFA mode that displays the translated message heads_up_message.ffa_collusion, and define the English translation string.

Estimated Code Review Effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🎮 A warning on the spawning ground,
"No deals before the fight!" we've found.
Fair-for-all means truly fair,
No secret teams in this shared air.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding an FFA collusion warning during spawn phase.
Description check	✅ Passed	The description is related to the changeset, explaining the purpose and referencing issue #3900 with supporting UI screenshot.
Linked Issues check	✅ Passed	The pull request fully addresses issue #3900 by adding a visible collusion warning message during FFA spawn phase to inform new users.
Out of Scope Changes check	✅ Passed	All changes are scoped to the FFA collusion warning: translation string addition and conditional HUD message rendering during spawn.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/client/hud/layers/HeadsUpMessage.ts`:
- Around line 185-186: In HeadsUpMessage.render (class HeadsUpMessage) guard
access to this.game before calling its methods: change the FFA warning condition
to first verify this.game exists (e.g. this.game && this.game.inSpawnPhase()) or
otherwise short-circuit when this.game is undefined; update any related checks
in render that reference this.game (including the spawn-phase/FFA expression and
any places that set isVisible via getMessage()) so initial Lit renders before
the controller injects game do not dereference this.game.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 69673d03-3983-445e-9d40-84f37d8e0ed4

📥 Commits

Reviewing files that changed from the base of the PR and between 5802c19 and 9799831.

📒 Files selected for processing (2)

• resources/lang/en.json
• src/client/hud/layers/HeadsUpMessage.ts

[evanpelle]

we should add a close button and only show this to a player once.

[Celant]

Also might be worth slightly softening the wording, so it sounds like a tip rather than a warning? Even just a "Remember: " at the start