Check-in [6708292b55]

Since the scan began recording islink and chnged 7/9, Create followed by Extract without Force failed on any repository with an "l" file: the file was missing, the scan read it as UNLINK, and the missing-file skip only covered plain edits.

Extract and Update now write a symlink entry as fossil's vfile_to_disk does: as a symlink to the blob content while allow-symlinks is on and the storage can make links, otherwise as a plain file holding the target. A symlink is deleted before a file is written over it, and setMergedMode leaves symlinks and directories alone, as file_setexe does. Extract's missing-file skip covers mode changes too, so the first Extract after Create plays fossil's open whatever the entry.

With allow-symlinks off, fossil itself reports such a file UNLINK and its checkout refuses without --force; Extract keeps that behavior, and an interop test pins it against fossil's open in both modes.

ScanENotFile no longer refuses a directory at a pending add or removal recorded with chnged=0, matching the else-if in vfile_check_signature.

Tracked in #449 check-in: 8cad365e82 user: [email protected] tags: feat/submanifest-reader, main, trunk