Polish: extract src/lib.rs so bins reuse a proper library crate

Historically every bin (claw-store, claw-cargo, claw-fuse)
re-declared the same 13-line 'mod ...' block at its own root.
Working but fragile — a new bin (or a new module) needed edits
in N+1 places and stayed one edit-slip away from silently
dropping something.

Now: src/lib.rs owns the shared module tree. Cargo.toml gets a
[lib] entry so cargo picks it up. claw_fuse.rs migrated as the
proof-of-concept — 13 mod lines → 4 use lines.

claw-store + claw-cargo bins still use their internal 'mod ...'
blocks and 'crate::...' paths — migrating them is mechanical
but noisy; deferred to a follow-on so this PR stays reviewable.
Both bins + tests continue to build unchanged.

387 tests pass.

claw-store/src/claw_fuse.rs

@@ -24,27 +24,13 @@ use std::ffi::OsStr;
 use std::path::PathBuf;
 use std::time::{Duration, UNIX_EPOCH};
 
-// Same module tree as main.rs / claw_cargo.rs — bin-only crate,
-// so we redeclare the mods here. Only `cluster::blob` is actually
-// used from this bin.
-mod actions;
-mod cargo_init;
-mod cluster;
-mod config;
-mod daemon;
-mod head_watch;
-mod hot;
-mod manifest;
-mod restore;
-mod serve;
-mod snapshot;
-mod sync;
-mod zfs;
-
-use cluster::blob::{BlobId, BlobStore};
-use cluster::refs::RefStore;
-use cluster::snapshot::SnapshotStore;
-use cluster::tags::TagStore;
+// Polish (2026-07-14): lib split. Bin pulls from the library crate
+// rather than re-declaring every internal module. Adds/removes to
+// the module tree happen in exactly one place (src/lib.rs).
+use claw_store::cluster::blob::{BlobId, BlobStore};
+use claw_store::cluster::refs::RefStore;
+use claw_store::cluster::snapshot::SnapshotStore;
+use claw_store::cluster::tags::TagStore;
 
 const TTL: Duration = Duration::from_secs(1);