Fix intra-doc link warnings; add clawsync-fs README and metadata

Doc fixes (20 warnings → 1 benign name-collision warning):
- clawsync-transport/quic.rs: QuicConfig::with_cert doesn't exist → backtick
- clawsync-onion/iblt.rs: bare `insert` link → backtick
- clawsync-core/lib.rs: simd_cdc is feature-gated → backtick
- clawhdf5-onion/annotation.rs: RevisionEntry/BranchEntry are in external
  clawhdf5-format crate, not re-exported → backtick
- clawhdf5-onion/gc.rs: compact_dead_epoch_revisions is private; flush links
  broken → backtick
- clawhdf5-onion/provenance.rs: RevisionEntry from external crate → backtick
- clawhdf5-onion/reader.rs: reconstruct_revision/revision_pages → Self:: prefix
- clawhdf5-onion/writer.rs: REV_FLAG_SNAPSHOT → crate::format:: path;
  reconstruct_revision → Self:: prefix
Remaining warning is `format` module/macro name collision — not a broken link.

clawsync-fs crate metadata:
- Add readme, keywords, categories to Cargo.toml
- Write README.md (CDC protocol diagram, module overview, usage examples)

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

crates/clawsync-transport/src/quic.rs

@@ -8,7 +8,7 @@
 //!
 //! For development / testing, use [`QuicConfig::self_signed`] which generates
 //! a temporary self-signed certificate.  Production deployments should use
-//! [`QuicConfig::with_cert`] with a properly-signed certificate.
+//! `QuicConfig::with_cert` with a properly-signed certificate.
 //!
 //! # Status
 //!