Closes M5 / M7 / M8a / M8b.
The optimized PathResolver and the read-side find_*_by_path queries
disagree on what counts as 'a path that hits a row'. After the drive-
refactor migration rewrote the path column to drop the
"My Folder - <user>/" prefix, files PUT through the WebDAV surface
stayed reachable by GET (legacy lookup) but vanished from the
optimized resolver (strict path-match). MOVE/DELETE/COPY 404'd on
every root-level file as a result.
Introduces resolve_or_legacy: optimized resolver first, then the
GET-style legacy lookups as a strict superset. Ownership is enforced
in both branches. handle_delete / handle_move / handle_copy each
collapsed from two near-identical resolver-only + legacy-only branches
into a single match using the helper — fewer lines, identical
semantics, root-level paths now resolve.
handle_copy also fixes M8b: copy_file_with_perms takes no destination
name, so a copy to a different filename in the same folder collided
with the source. After the copy, rename the new file when dest_name
differs from source name. Mirrors what handle_move already does.
Edouard Vanbelle
5e1c99e227