Keep XML references from truncating WebDAV file paths

[Maya-Kid]

Problem

A WebDAV file named A&B.txt can be silently skipped during synchronization. A valid PROPFIND response represents its path as /docs/A&B.txt. quick-xml emits text, a reference, and more text separately, but the parser overwrites href on every text event and ignores references. The resulting path is only B.txt; the subsequent GET targets /B.txt and a 404 is treated as an unreadable file.

Change

Accumulate text, character/entity references, and CDATA until the field closes, then interpret href, content length, and last-modified values. Percent decoding runs after the full href is assembled. Whitespace is trimmed at field boundaries rather than between XML fragments. Unknown properties remain ignored; no new dependency or API/schema change.

Reproduction and validation

Base: 816d4a39255b68849d9eecaf273ec32b3f7d793d (dev).

• Parser regression covers &, decimal/hex character references, CDATA, and mixed text/CDATA. On baseline the href is B.txt instead of /docs/A&B.txt.
• End-to-end regression invokes the real fetch against a local HTTP fixture: the original implementation returns zero files; the fixed implementation downloads the expected file and retains its filename, bytes, and external key.
• Before: 2 regression failures, 4 existing tests passed. After: all 6 passed.
• cargo +1.98.1 test -p utopia-server --locked webdav::tests:: -- --skip it_reads_from_a_real_webdav_server
• Workspace cargo fmt --all --check and cargo clippy --workspace --all-targets --locked -- -D warnings: passed.
• git diff --check: passed.

The optional externally configured WebDAV server test was explicitly excluded; the local HTTP integration test did run. No existing deployment, credentials, or database were used. Full workspace runtime tests were not repeated for this patch.