Fix wrong error wording for flag-only providers in setup wizard

[gantoine]

Description
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The setup wizard's metadata step (step 3) showed "API key invalid" for any enabled provider that failed its heartbeat probe, including flag-only providers like PlayMatch and Hasheous that have no API key. This contradicted the Settings → Metadata sources view, which already adapts its status wording per provider (key-based vs flag-only).

This PR mirrors that behavior in SetupStepMetadata.vue:

• Adds a requiresKey flag to each source (matching MetadataSources.vue).
• Flag-only providers (LaunchBox, Flashpoint, HowLongToBeat, Hasheous, PlayMatch) now use connection-oriented wording:
  • Failed probe → "Unreachable" (instead of "API key invalid")
  • Disabled → "Provider disabled" with a plug-off icon (instead of "API key missing")
• Key-based providers are unchanged.

Reuses existing locale keys (metadata-status-unreachable, metadata-status-disabled), so no new translations are needed. This addresses the messaging inconsistency reported; the underlying PlayMatch availability problem is tracked separately in #3764.

AI assistance: this change was written with the help of Claude Code (investigation, implementation, and verification). All changes were reviewed by the author.

Checklist
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• I've tested the changes locally
• I've updated relevant comments
• I've assigned reviewers for this PR
• I've added unit tests that cover the changes

Screenshots (if applicable)

Fixes #3795

🤖 Generated with Claude Code

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[greptile-apps]

Greptile Summary

This PR gives flag-only metadata providers accurate status wording in the setup wizard. The main changes are:

• Classifies each provider as key-based or flag-only.
• Shows “Provider disabled” for disabled flag-only providers.
• Shows “Unreachable” when a flag-only provider fails its probe.

Confidence Score: 5/5

This looks safe to merge.

• Every provider initializes the new required field.
• Provider classifications match the existing Metadata Sources settings view.
• The referenced status translations already exist.
• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
frontend/src/v2/components/Auth/SetupStepMetadata.vue	Adds provider classification and selects disabled or failed-probe labels based on whether an API key is required.

_{Reviews (1): Last reviewed commit: "Fix wrong error wording for flag-only pr..." | Re-trigger Greptile}