fix(914): thread-local ALL_OPS/VECTOR_CLOCK in cfg(test) so compaction tests don't race

Root cause was not the persist channel (the test-mode channel is unbounded
and its receiver is leaked, so sends never fail). It was that `ALL_OPS` and
`VECTOR_CLOCK` were process-wide `OnceLock` globals while `CRDT_STATE` was
already thread-local — so one test thread's `apply_compaction` would prune
another test thread's freshly-written ops out of the shared journal, and
the subsequent `all_ops_json()` read in `compaction_reduces_ops` would
return fewer than the 5 it had just written.

Mirror the pattern already used for `CRDT_STATE` and `SnapshotState`: in
`cfg(test)` use thread-local `OnceLock<Mutex<...>>`s for the op journal and
vector clock, accessed via new `all_ops_lock()` / `vector_clock_lock()`
helpers. Production code path is unchanged (still the global statics set
during `init()`).

Touches ops/read/snapshot call sites to go through the helpers. Note in
passing that this overlaps backlog story 518; that story is about the
production-side persist path, this is the cfg(test)-only journal-isolation
slice.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/crdt_state/mod.rs

@@ -60,7 +60,7 @@ pub use write::{
 #[cfg(test)]
 pub use state::init_for_test;
 
-pub(crate) use state::{ALL_OPS, VECTOR_CLOCK};
+pub(crate) use state::{all_ops_lock, vector_clock_lock};
 
 /// Hex-encode a byte slice (no external dep needed).
 pub(crate) mod hex {