feat: Phase 5-6 — CREATE VIEW, migrations, deadlock detection, JSON logging, admin UI

Phase 5 — ERP Features:
- CREATE VIEW name AS SELECT ... — parser + executor with view expansion
- DROP VIEW — parser + executor
- CREATE MIGRATION name AS 'sql' — parser + executor, stored in LSM-Tree
- APPLY MIGRATION name — parser + executor, replays stored migration SQL
- Views table in ExecutionContext, expanded on SELECT FROM view

Phase 6 — Production Readiness:
- Deadlock detection: timeout-based auto-abort for stale transactions (30s default)
- TxnManager.txnTimeoutMs configurable
- Structured JSON logging module (logging.nim) with levels: debug/info/warn/error
- Admin dashboard Web UI at GET /admin — SQL playground, schema browser, metrics
- Dark theme HTML/CSS with tabs

Lexer: added tkView, tkMigration, tkApply tokens
Parser: parseCreateView, parseDropView, parseCreateMigration, parseApplyMigration
AST: nkCreateView, nkDropView, nkCreateMigration, nkApplyMigration nodes

All 216 tests pass

src/barabadb/core/mvcc.nim

@@ -42,14 +42,15 @@ type
     nextLsn: uint64
     activeTxns: Table[TxnId, Transaction]
     committedTxns: seq[TxnId]
-    globalVersions*: Table[string, seq[VersionedRecord]]  # key -> versions
+    globalVersions*: Table[string, seq[VersionedRecord]]
+    txnTimeoutMs: int64
 
 proc `==`*(a, b: TxnId): bool {.borrow.}
 proc `==`*(a, b: Lsn): bool {.borrow.}
 proc `$`*(id: TxnId): string = $uint64(id)
 proc `$`*(lsn: Lsn): string = $uint64(lsn)
 
-proc newTxnManager*(): TxnManager =
+proc newTxnManager*(txnTimeoutMs: int64 = 30000): TxnManager =
   new(result)
   initLock(result.lock)
   result.nextTxnId = 1
@@ -57,6 +58,7 @@ proc newTxnManager*(): TxnManager =
   result.activeTxns = initTable[TxnId, Transaction]()
   result.committedTxns = @[]
   result.globalVersions = initTable[string, seq[VersionedRecord]]()
+  result.txnTimeoutMs = txnTimeoutMs
 
 proc allocTxnId(tm: TxnManager): TxnId =
   result = TxnId(tm.nextTxnId)
@@ -157,6 +159,14 @@ proc write*(tm: TxnManager, txn: Transaction, key: string, value: seq[byte]): bo
     release(tm.lock)
     return false
 
+  # Timeout-based deadlock detection: abort stale transactions
+  let now = getMonoTime().ticks()
+  for otherId, otherTxn in tm.activeTxns:
+    if otherId != txn.id and otherTxn.state == tsActive:
+      if now - otherTxn.startTime > tm.txnTimeoutMs * 1_000_000:
+        otherTxn.state = tsAborted
+        tm.activeTxns.del(otherId)
+
   # Check for write-write conflict
   if key notin txn.writeSet:
     if key in tm.globalVersions: