fix(files): improve upload error handling for DAV responses

[joshtrichards]

• Resolves: Error shown when file upload receives 403 references "access control" + never includes any additional explanation text sent on by server(s) #48164

Summary

Improve upload error handling in apps/files/src/views/FilesList.vue by parsing the DAV error payload before falling back to generic HTTP status handling.

This fixes cases where the frontend currently assumes:

• any 403 means access control blocked the operation
• any 404 or 409 means the target folder no longer exists

In practice, the DAV backend may include structured XML with more specific details such as:

• s:exception
• s:message
• o:reason
• o:retry
• o:hint

This change makes the upload error handling more accurate by:

• parsing DAV XML first when available
• only showing the access-control-specific message when the DAV payload confirms that case
• preferring DAV-provided error details over generic 404 / 409 assumptions
• keeping generic fallback messages only when the response body does not provide anything better

Changes

• add DAV error parsing helper(s) in FilesList.vue
• detect access-control-specific 403 responses using the DAV exception payload
• prefer o:reason / s:message over generic status-only messaging
• keep 404 / 409 target-folder messaging as a fallback only
• extend the quota/size-related upload handling to also account for 413

Follow-up note

There is a likely backend contract inconsistency worth reviewing separately:

• OCP\Files\NotEnoughSpaceException is currently converted in DAV to EntityTooLarge / HTTP 413
  • see Quota wrapper fixes #59995
• semantically, insufficient storage may be better represented as 507 Insufficient Storage
• if the backend intentionally keeps returning 413, it would be helpful to provide structured DAV payload hints so clients can reliably distinguish:
  • file too large
  • insufficient remaining space / quota

This PR does not change the backend contract; it only makes the frontend more robust against the current behavior.

TODO

• See if E2E/integration need to be adjusted
• Possibly backport to v34

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[joshtrichards]

/compile

[joshtrichards]

/compile