lib9p: unify 9P client — ollie-9p now imports lib9p/client instead of duplicating it
- Extract shared 9P operations (Dial, Read, Write, Rdwr, Stat, Ls, Create, Remove, Mkdir, Rename, ModeString) into lib9p/client package
- lib9p/lib9p.go (C FFI layer) delegates to lib9p/client for all operations
- cmd/ollie-9p/main.go uses lib9p/client directly, eliminating ~250 lines of duplicated dial/open/write/close boilerplate
- Removed lib9p/go.mod and go.sum (no longer a separate module; lives in main module)
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