[AlexAndBear]

Description

• Error messages: On servers without TUS, failed uploads now show the real reason ("This item is locked", "Quota exceeded" or the server's message) instead of always "Unknown error".
• Retries: Failed non-TUS uploads are only retried on network errors now, not on every 4xx/5xx response, so a full quota or a locked target doesn't upload the whole file three more times. This matches what we already do for TUS.

Related Issue

• Fixes Uploads without TUS always fail with "Unknown error" #4232

How Has This Been Tested?

• test environment: unit tests (Vitest), browser tests (Playwright) against a local OpenCloud
• test case 1: unit: xhr upload errors with 423, 507 and a 500 with a server message show the right text, an empty 500 shows Unknown error; xhr retries only on status 0
• test case 2: browser (TUS disabled via mocked capabilities): 423 on file and folder, 507, 500 with message, empty and HTML 500 show the right messages with one request each, network aborts are still retried; TUS uploads and a TUS 507 unchanged

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)