v1.1.7: deep security & reliability audit — 33 bugs fixed

Critical (5):
- Reject empty JWT secret when authEnabled (server.nim)
- Fix 2PC marking uncontacted participants as prepared/committed (disttxn.nim)
- Fix Raft commit index calculation for even-sized clusters (raft.nim)
- Fix REP/DISTTXN protocol auth bypass (server.nim)
- Fix HTTP backup/restore path traversal (httpserver.nim)

High (11):
- Fix WAL write race with flush (lsm.nim)
- Fix MVCC savepoint/rollback deep-copy writeSet (mvcc.nim)
- Fix table mutation during deadlock iteration (mvcc.nim)
- Fix LIMIT 0 returning all rows (executor.nim)
- Fix COUNT(col) counting NULL values — 3 locations (executor.nim)
- Fix EXISTS subquery lowering missing subqueryPlan (executor.nim)
- Fix Raft appendEntries/applyCommitted array vs logical index (raft.nim)
- Fix timing attacks on constantTimeCompare and SCRAM (auth.nim, scram.nim)
- Fix B-tree leaf merge phantom separator key (btree.nim)
- Fix SSL verifyPeer not applied to newContext (ssl.nim)
- Fix sharding connectWithTimeout missing SO_ERROR check (sharding.nim)
- Fix sync replication returning success on partial ack (replication.nim)
- Fix WebSocket JWT expiration not validated (websocket.nim)

Medium (13):
- Fix writeSSTable partial file → tmp + atomic rename (lsm.nim)
- Fix multi-CTE table loss (executor.nim)
- Fix nl_to_sql DML restricted to superuser (executor.nim)
- Fix unbounded plan cache — max 10000 (adaptive.nim)
- Fix migration lock crash persistence — timestamp + stale detection (executor.nim)
- Fix admin panel auth (httpserver.nim)
- Fix MVCC unbounded txn tracking — prune in compactVersions (mvcc.nim)
- Fix connection pool maxLifetime check (pool.nim)
- Fix JWT JSON parser backslash escapes (auth.nim)
- Fix substr(s, start) returning single char (udf.nim)
- Fix loadSSTable minimum file-size check (lsm.nim)
- Fix compaction mmap leak (compaction.nim)
- Fix JSON injection in hybrid_search_filtered (executor.nim)

Low (4):
- Raft loadState logs error instead of silent discard
- Replication healthCheck double-close fixed
- Lexer readIdent double column counting fixed
- WebSocket frame 32-bit overflow guard

All 448 tests passing, 0 failures. Bump version to 1.1.7.

src/barabadb/protocol/auth.nim

@@ -100,11 +100,12 @@ proc hmacSha256(key, message: string): string =
   return $outerHash
 
 proc constantTimeCompare(a, b: string): bool =
-  if a.len != b.len:
-    return false
-  var diff = 0
-  for i in 0..<a.len:
-    diff = diff or (ord(a[i]) xor ord(b[i]))
+  let n = max(a.len, b.len)
+  var diff = a.len xor b.len
+  for i in 0..<n:
+    let ca = if i < a.len: ord(a[i]) else: 0
+    let cb = if i < b.len: ord(b[i]) else: 0
+    diff = diff or (ca xor cb)
   return diff == 0
 
 # ---------------------------------------------------------------------------
@@ -159,8 +160,18 @@ proc verifyToken*(am: AuthManager, token: string): (bool, JWTClaims) =
       if i < payload.len and payload[i] == '"':
         inc i
         while i < payload.len and payload[i] != '"':
-          val &= payload[i]
-          inc i
+          if payload[i] == '\\' and i + 1 < payload.len:
+            case payload[i+1]
+            of '"': val &= '"'
+            of '\\': val &= '\\'
+            of '/': val &= '/'
+            of 'n': val &= '\n'
+            of 't': val &= '\t'
+            else: val &= payload[i+1]
+            inc i; inc i
+          else:
+            val &= payload[i]
+            inc i
         inc i
       elif i < payload.len and payload[i] in {'0'..'9', '-'}:
         while i < payload.len and payload[i] notin {',', '}'}: