refactor: use actual svg in networks util package

[Julink-eth]

Explanation

The shared Asset component's fallback icon was defined as an inline QUESTION_MARK_SVG string constant (600+ characters of SVG markup) in Asset.tsx, because at the time of #418 the library could not bundle .svg imports. #423 fixed that: the library now supports importing .svg files as strings, copies them to dist/, and ships a Jest transformer for them.
This PR switches the fallback to that mechanism:

• Adds src/ui/Asset/question-mark.svg (the same question-mark markup as Stellar's src/ui/images/question-mark.svg), colocated with its only consumer.
• Replaces the inline QUESTION_MARK_SVG export in Asset.tsx with import questionMarkIcon from './question-mark.svg', and uses it as the AssetIcon fallback.
• Updates the fallback test to import the same file and assert its markup in the serialized output.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

🟢 Approval recommended

The focused refactor preserves behavior and is covered by the existing fallback tests.

0 open findings

What changed in this PR

Replaces the shared AssetIcon fallback’s inline SVG constant with a bundled SVG asset.

Changes:

• Adds the question-mark SVG asset.
• Imports it as the fallback icon.
• Updates fallback tests to use the SVG import.

File	Description
packages/​snap-networks-utils/​src/​ui/​Asset/​question-mark.svg	Adds the fallback icon asset.
packages/​snap-networks-utils/​src/​ui/​Asset/​Asset.tsx	Uses the imported SVG as the fallback.
packages/​snap-networks-utils/​src/​ui/​Asset/​Asset.test.tsx	Updates fallback assertions.

🧠 Review effort: Balanced

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