fix: resolve all 55 identified bugs across the codebase

Comprehensive bug fix pass across all subsystems:
- Critical: lexer infinite loop, WAL lock discipline, checkpoint safety,
  compaction verification, HMAC key truncation, healthCheck leak
- High: MVCC lock safety, B-Tree delete rebalancing, Raft stale term
  handling, replication socket leaks and ack cleanup, sharding migration
  with old assignments, 2PC recovery, JWT/SCRAM auth fixes, wire protocol
  bounds checks
- Medium: config error handling, MERGE parser completeness, IR/codegen
  correctness, UDF bounds checks, LIMIT cost accuracy, mmap safety
- Low: timeout handling, float parsing edge cases, uint32 truncation,
  cache entry cleanup

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/barabadb/query/ir.nim

@@ -293,10 +293,10 @@ proc inferExpr*(tc: TypeChecker, expr: IRExpr, context: Table[string, IRType]):
     if operandType == nil:
       return nil
     case expr.unOp
-    of irEq, irNeq, irLt, irLte, irGt, irGte, irAnd, irOr, irNot,
-       irIsNull, irIsNotNull, irIn, irNotIn, irLike, irILike, irBetween,
-       irFtsMatch:
+    of irNot, irIsNull, irIsNotNull:
       return IRType(name: "bool", kind: itkScalar)
+    of irNeg:
+      return operandType
     else:
       return nil
   of irekBinary: