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/ast.nim

@@ -20,6 +20,10 @@ type
     nkCommitTxn
     nkRollbackTxn
     nkExplainStmt
+    nkCreateView
+    nkDropView
+    nkCreateMigration
+    nkApplyMigration
 
     # Clauses
     nkFrom
@@ -200,6 +204,18 @@ type
     of nkExplainStmt:
       expStmt*: Node
       expAnalyze*: bool
+    of nkCreateView:
+      cvName*: string
+      cvQuery*: Node
+      cvOrReplace*: bool
+    of nkDropView:
+      dvName*: string
+      dvIfExists*: bool
+    of nkCreateMigration:
+      cmName*: string
+      cmBody*: string
+    of nkApplyMigration:
+      amName*: string
     of nkCreateIndex:
       ciTarget*: string
       ciName*: string