docs: update README and all docs with formal verification, new BaraQL features, OpenTelemetry tracing

- Add Formal Verification section to README and architecture docs
- Document TLA+ specs for Raft, 2PC, MVCC, Replication
- Add new BaraQL features: JSON path (->, ->>), FTS @@, CREATE INDEX USING FTS,
  RECOVER TO TIMESTAMP, UNION/INTERSECT/EXCEPT
- Add OpenTelemetry tracing example to README
- Update Quick Start to use nimble test/bench
- Update EN and BG documentation

docs/en/transactions.md

@@ -58,4 +58,21 @@ Nested transaction savepoints:
 tm.savepoint(txn, "sp1")
 # ... operations ...
 tm.rollbackToSavepoint(txn, "sp1")
+```
+
+## Formal Verification
+
+The MVCC / Snapshot Isolation protocol is formally specified in TLA+:
+
+- **Spec:** `formal-verification/mvcc.tla`
+- **Verified properties:**
+  - `NoDirtyReads` — transactions never read uncommitted data
+  - `ReadOwnWrites` — transactions always see their own writes
+  - `WriteWriteConflict` — first-committer-wins (no two committed transactions write the same key)
+
+Run TLC locally:
+
+```bash
+cd formal-verification
+java -cp tla2tools.jar tlc2.TLC -config models/mvcc.cfg mvcc.tla
 ```