[pull] master from mattermost:master - #926

* Improve plugin upload dropzone UX

Co-authored-by: Ben Schumacher <hanzei@users.noreply.github.com>

* Refine plugin upload dropzone presentation

Co-authored-by: Ben Schumacher <hanzei@users.noreply.github.com>

* Update plugin upload Cypress specs

Co-authored-by: Ben Schumacher <hanzei@users.noreply.github.com>

* Preserve plugin upload drag state over children

Co-authored-by: Ben Schumacher <hanzei@users.noreply.github.com>

* Show plugin manifest name in upload success message

The success toast previously interpolated the raw uploaded filename
(e.g. mattermost-plugin-fl3xx-v0.8.1-linux-amd64.tar.gz), which is not
meaningful to admins. Use the plugin manifest name returned by the
upload response instead, falling back to the filename if unavailable.

* Indicate upgrade/downgrade/same-version on plugin overwrite

State whether an overwritten plugin's success message represents an
upgrade, downgrade, or same-version replace, comparing the previously
installed manifest version with the newly uploaded one via semver.

* Refine plugin upload dropzone presentation and uploading state.

Use a native button with Compass upload icon, keep progress inside the dropzone without changing height, and reserve button color for hover/drag-active.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Show selected filename in the dropzone and improve upload status messaging.

Keep success/error feedback aligned with the dropzone, with a green check or red alert icon beside the message.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Fix no-nested-ternary lint error in plugin upload dropzone

Extract the upload dropzone title text into a helper method to
satisfy eslint's no-nested-ternary rule.

* Fix stylelint order/properties-order errors in plugin_management.scss

* Add unit tests for formatUploadOverwriteMessage semver paths

Covers the upgrade, downgrade, same-version, and fallback
(missing/invalid semver) branches, which the automated test-analysis
bot flagged as untested.

* Add unit tests for remaining disabled-reason branches and file drop

Covers renderUploadDisabledReason's isDisabled and !enable branches,
and adds a fireEvent.drop test for handleUploadDrop, closing out the
remaining gaps from the automated test-analysis review.

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Ben Schumacher <hanzei@users.noreply.github.com>
Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Matthew Birtch <2040554+matthewbirtch@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>