brygge-decode-svn

brygge's Subversion source decoder: reads an SVN history from a dumpstream (a user-supplied dumpfile, or a read-only local `svnadmin dump`) and produces a brygge-ir IR — a Stated linear spine with Stated copies, plus an opt-in Derived branch/tag layer. Pure Rust, no linked SVN library (RFC 006 Tier D). The one crate that reads SVN (RFC 009 D-1).