fix(getImageUrl): strip trailing slash from assetsImagesPath to prevent double slashes

[roshinit-a]

Description

getImageUrl() in web-components/src/signals/app.ts produces URLs with double slashes when assetsImagesPath ends with a trailing / (e.g. set by an integrating app via assetsImagesPath.set("/assets/")).

// Before fix:
assetsImagesPath.set("/assets/")
getImageUrl("logo.png") // → "/assets//logo.png" ❌

// After fix:
getImageUrl("logo.png") // → "/assets/logo.png" ✅

The bug was already acknowledged in app.test.ts with the comment "// Double slash - might be a bug in implementation", but the test was accepting the broken output.

Fix in app.ts:

-  return `${assetsImagesPath.get()}/${fileName}`
+  return `${assetsImagesPath.get().replace(/\/+$/, "")}/${fileName}`

Fix in app.test.ts:

• Replaced the broken test (which expected /assets//image.png) with a proper regression test that asserts /assets/image.png
• Added a test for multiple trailing slashes (/assets///)
• Added a test for CDN URLs with trailing slashes

Screenshot or video

No visual changes — logic fix.

Related issue(s) and discussion

• Fixes: Bug: getImageUrl() produces double slashes when assetsImagesPath has a trailing slash #473

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Checklist: Author Self-Review

• I have performed a self-review of my own code (including running it).
• I understand the changes I'm proposing and why they are needed.
• My changes generate no new warnings or errors (linting, console).
• I have made corresponding changes to the documentation (if applicable).

Large Language Models usage disclosure

• Generic LLM v0.0.0

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