fix(dashboard): display dashboard images configured via external URL link

[deaflynx]

Summary

Merges the CE fix (thingsboard/flutter_thingsboard_app#249) from ce-origin/fix/dashboard-image-external-url-link, plus one PE-side resolution noted below.

Dashboard cards on the Home grid showed an empty white box instead of the thumbnail when the dashboard image was configured via the "Image link" field. Images uploaded to the Image Gallery displayed fine.

Fixes PROD-8502.

Two distinct inputs produced the same empty box, and both are fixed here:

1. An external web URL — https://example.com/pic.png
2. An image public link copied from the gallery — /api/images/public/{key}, found while reviewing (1) and reproduced on a device

Root cause

The platform stores every dashboard image value with a tb-image; prefix, external URLs included (prependTbImagePrefix in gallery-image-input.component.ts). Utils.imageFromTbImage computed the prefix-stripped URL but only used it in the gallery-resource branch, while the base64 and external-URL branches checked and loaded the raw prefixed string. Uri.tryParse('tb-image;https://…') returns null, so external links fell through to the error placeholder — a transparent 1×1 GIF stretched by the card's FittedBox, which renders as the empty white box.

The public-link case has a separate cause. TbResourceInfo.getPublicLink() returns a relative path, the "Embed image" dialog hands users exactly that string, and the "Image link" field has no validators. IMAGES_URL_REGEXP matches only tenant|system, so a public link is classified as external, and _isValidUrl — which was just Uri.tryParse(url) != null and therefore true for almost any string — let the relative path reach Image.network, where it cannot be fetched at all (ArgumentError: No host specified in URI).

Changes

• Use the prefix-stripped URL in every branch, and rename it to resolvedImageUrl to match ImageService.resolveImageUrl on the web side.
• Anchor the tb-image; strip with startsWith/substring instead of replaceFirst, so an occurrence inside a link is no longer removed.
• Replace _isValidUrl with _resolveNetworkImageLink, which classifies and resolves in one step: absolute http/https links are fetched as they are, platform-relative links resolve against the active endpoint the way a browser resolves them against its origin, and anything without a meaningful target renders the missing image. Resolved relative links carry no auth header, matching the platform — /api/images/public/{key} is a noauth endpoint and a browser <img src> does not send the JWT either.

Since imageFromTbImage also backs device and device-profile images, this repairs image links there too, not only the dashboard grid.

Behaviour

Value in "Image link"	Result
https://example.com/pic.png	fetched as is
tb-image;https://example.com/pic.png	prefix stripped, fetched
/api/images/tenant/pic.png	endpoint + path, with auth header
/api/images/public/pic.png	endpoint + path, no auth header
data:image/png;base64,…	decoded in memory
ftp://…, or text that is not a link	missing image placeholder

Test plan

• Dashboard image set via an external URL → thumbnail displays on the Home grid
• Dashboard image set to an image public link copied from the gallery Embed dialog → thumbnail displays
• Dashboard image uploaded to the Image Gallery → still displays
• Dashboard without an image → placeholder icon still displays
• Device and device profile images still display

PE-specific note

The merge conflicted in lib/utils/utils.dart, in the image-resource branch that PE rewrote for the whitelabel login logo. Resolved by keeping the PE loginLogo structure and taking the rename to resolvedImageUrl.

That resolution also brings PE's _isImageResourceUrl check onto the prefix-stripped value, where it was previously testing the still-prefixed string. Behaviour is unchanged today, because _imagesUrlRegexp is unanchored and matches with or without the prefix — but it puts PE in line with CE and is a prerequisite for anchoring that pattern, which would otherwise classify every gallery image as external in PE.