fix(ocdav): encode oc:downloadURL path so filenames with "%" round-trip

[michaelstingl]

Description

PROPFIND builds the oc:downloadURL property with url.JoinPath, which treats a literal % in a filename as an escape. A name like firstword%20secondword.pdf is read as firstword secondword.pdf, so the web "Download" button requests the wrong path and the download returns 404 from personal/space storage. The sibling href in the same response uses net.EncodePath and stays correct, so PROPFIND already emits a correct href next to an under-encoded oc:downloadURL.

The fix uses net.EncodePath(path), the encoder the href already uses, in downloadURL (internal/http/services/owncloud/ocdav/propfind/propfind.go). url.JoinPath was introduced here to keep a literal # working (see #415); net.EncodePath covers both # -> %23 and % -> %25, so it keeps that behavior while letting names with reserved characters round-trip. The GET handler and the proxy are unchanged; only the URL this property emits was wrong.

Related Issue

• Fixes Cannot download files that have "%20" in their filename. opencloud#2852

Motivation and Context

A file whose name contains a literal % cannot be downloaded from personal or space storage via the web UI, although it lists and opens normally. Public links are unaffected: the public-files handler resolves the file by share token and emits no oc:downloadURL.

How Has This Been Tested?

• test environment: reva main, Go 1.26, local
• go build, go vet, go test ./...propfind/... and .../net/..., and the pinned golangci-lint v2.10.1 (make lint): all pass, 0 lint issues
• the fix, unit: new ginkgo DescribeTable for downloadURL asserts a literal % encodes to %25 (whether or not followed by hex digits), # to %23, a plain space to %20
• the fix, over HTTP: on a local revad stack, patched vs unpatched, PROPFIND of a public link to a file named firstword%20secondword.pdf emits an oc:downloadURL ending ...firstword%2520secondword.pdf with the fix and ...firstword%20secondword.pdf without it

Screenshots (if appropriate):

n/a. Server-side URL-encoding fix.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added (the behat suite has no download-of-a-name-with-reserved-characters scenario; this PR covers it at the unit level. A behat scenario can follow in the opencloud repo.)
• Documentation added (n/a — reva generates the changelog from the PR title + Type:* label via ready-release-go; no fragment needed)

_{🤖 drafted with Claude Code, reviewed before submitting.}

[micbar]

Please remove the changelog item. We are using ready-release-go from woodpecker.

[michaelstingl]

@micbar done, removed the changelog commit. The fix commit is unchanged.

_{🤖 drafted with Claude Code, reviewed before submitting.}