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/query/lexer.nim

@@ -90,6 +90,9 @@ type
     tkCommit
     tkRollback
     tkExplain
+    tkView
+    tkMigration
+    tkApply
     tkCount
     tkSum
     tkAvg
@@ -233,6 +236,9 @@ const keywords*: Table[string, TokenKind] = {
   "commit": tkCommit,
   "rollback": tkRollback,
   "explain": tkExplain,
+  "view": tkView,
+  "migration": tkMigration,
+  "apply": tkApply,
   "count": tkCount,
   "sum": tkSum,
   "avg": tkAvg,