Show the Runner Gallery link in an info popover

[Kyome22]

Context of Contribution

• Bug Fix
• Refactoring
• New Feature
• Localization (new language or translation update)
• Others

Summary of the Proposal

The Custom Runners section carried the Runner Gallery link in a section footer built from an AttributedString, which located the substring "Runner Gallery" at runtime and styled the link range by hand. That approach breaks silently whenever a translation does not contain the literal "Runner Gallery".

This PR moves the link behind an info button, matching the affordance the Custom Metrics section already had:

• CustomRunnerSettings gains showingInfoPopover and an infoButtonTapped Action; the footer is replaced by an info.circle button with a popover holding runnerGalleryDescription and a real Link to the gallery.
• CustomMetricsSettings renames showingHelpPopover / helpButtonTapped to showingInfoPopover / infoButtonTapped, so both sections name the affordance after the button the user actually taps.
• Both info buttons now use a Label with .labelStyle(.iconOnly), so the icon carries an accessibility label instead of being an unlabeled Image.
• In CustomMetricsSettingsSectionView, .fileImporter and .confirmationDialog move onto the views that actually own them (the add button and the list) instead of hanging off the enclosing HStack/List.
• New string keys: information and viewRunnerGallery.
• Store tests cover infoButtonTapped for both stores.

Reason for the new feature

N/A — this is a refactor of an existing affordance, not a new feature.

Verification

Xcode build succeeded, and the UnitTest test plan passes in full: 172 tests, 172 passed, 0 failed.

Checklist

• I have read the CONTRIBUTING.md and agree to follow it.
• This PR does not contain commits of multiple contexts.
• The diff is minimal — no unrelated refactors, whitespace churn, or drive-by cleanups.
• Code follows proper indentation and naming conventions.
• Layering follows the LUCA architecture: no logic in DependencyClient, no logic in UserInterface views, no Asset/String Catalog references from Model.
• Implemented using only APIs that can be submitted to the App Store.
• Localization PRs only: Every translated string in this PR was hand-crafted by a human translator. No machine translation or LLM output was used. See CONTRIBUTING.md → Localization.

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