Back up local files before overwriting during ConflictRemoteWins so data
is never silently lost. Fix false-positive change detection by parsing
timestamps before comparing (different formats like RFC3339 vs HTTP date
were never equal as strings). Add zeroize crate to zero WebDAV credentials
in memory on drop, preventing exposure in core dumps.
Restrict is_syncable() to validate path depth: .md files and .listdata.json
must be at depth 2 (inside list dirs), .metadata.json only at depth 1 (root).
Prevents syncing arbitrary files at unexpected depths. Back up corrupted
sync queue files before resetting, and log warnings on parse failures
instead of silently dropping queued operations.
Tristan Michael