Remove entries through opaque directory grants #429

Scope

Implement FileSystemDirectoryHandle.removeEntry(name, { recursive }) over a typed opaque native directory-mutation authority.

Required browser behavior:

• remove a regular file or empty directory when recursive is false;
• remove a directory tree when recursive is true;
• reject a missing child with NotFoundError and a non-empty directory without recursion with InvalidModificationError;
• preserve WebIDL-shaped receiver, option conversion, and invalid single-component TypeError behavior;
• map cancellation, denial, changed/stale generation, capacity, and I/O outcomes to browser-compatible errors;
• bind each request to the calling realm/origin/profile/partition, complete exactly once, and retire it on navigation/runtime teardown.

Product dependency

Unchanged VS Code calls this operation from htmlFileSystemProvider.delete() and uses delete while implementing browser file/folder rename as copy plus removal. This is the smallest remaining generic File System Access gap on the current main branch.

Acceptance

• pinned File System Access spec/WPT and direct Chrome oracle for file, empty directory, recursive tree, missing, non-empty, Unicode and invalid names;
• native ABI/export/C11 and exact AppScene adapter parity;
• origin/profile/partition security, symlink/race behavior, cancellation, stale generation, and navigation retirement;
• 10,000 bounded broker operations and 100 lifecycle cycles with heap/RSS/FD bounds;
• unchanged Code OSS call-site evidence for delete and rename.

Blocked by the missing native opaque removal authority tracked in SceneTech/AppScene. This issue excludes move/rename, CSS, MessagePort #288, webviews/resources #266, packaging, consolidation PR #76, and vscode-demo.

Parent: #248.