The legacy Export Platforms dialog was replaced by a standalone Dashio HTML/JavaScript screen backed by a session-authenticated PHP BFF.

• gui/templates/platforms/platformsExport.html provides project context, platform count, XML format, filename validation, Back/Cancel/Refresh actions, documentation link, locale switcher, loading state, and explicit empty, authentication, permission, and project error states.
• api/platformsexport/index.php exposes init and download actions, validates the TestLink session and Test Project, checks platform_view or platform_management access, safely sanitizes download filenames, and returns the same TestLink XML fields as the legacy exporter.
• gui/templates/platforms/platformsView.html now launches the standalone screen and retains the project and plan context.
• lib/functions/common.php registers the platformsExport action.
• All pexp.* labels are present in all 10 client-side i18n bundles.

Scenario	Result
Project with two platforms	Export launcher loads and reports 2 defined
Empty filename	Browser validation blocks export
Unsafe filename	a/b name <regression>.xml downloads as a_bname_regression_.xml
Populated XML	Valid XML; both platforms and five legacy platform fields present
Empty project	Warning shown; valid XML with zero platforms downloaded
Romanian locale	Screen labels render in Romanian
Invalid project	Structured error and Back action shown
Anonymous session	BFF returns 401; session-expired state shown
Insufficient rights	BFF returns 403; permission-denied state shown

Browser verification used disposable Test Projects PEXPR and PEMPTY. No unexpected JavaScript exceptions or new PHP Error/Warning output were observed.

Suite 1583 — Platforms Export standalone screen and BFF was added to tmp/TLU_Test_Cases.md: 9/9 PASS.

• api/platformsexport/index.php — export initialization and XML download BFF
• gui/templates/platforms/platformsExport.html — standalone Dashio screen
• gui/templates/platforms/platformsView.html — live launcher wiring
• lib/functions/common.php — shared action registration
• gui/templates/i18n/*.json — localized pexp.* keys

Refs #1583.