feat: Session 10.3 MCP Server + Session 11 Graph Engine Deep Integration

MCP Server (10.3):
- STDIO JSON-RPC 2.0 transport with 3 AI tools: query, vector_search, schema_inspect
- Multi-tenant session vars (tenant_id, user_id) with RLS support
- Standalone binary: build/baramcp
- Tested with all 3 tools + parameterized queries + vector search + schema inspect

Graph Engine Deep Integration (Session 11):
- CREATE GRAPH / DROP GRAPH DDL support
- Graph engine wired to SQL executor via GRAPH_TABLE() function
- 7 algorithms: BFS, DFS, PageRank, ShortestPath, Dijkstra, Louvain, Community
- INSERT into _nodes/_edges tables auto-syncs with native Graph adjacency lists
- Optional MATCH pattern, ALGORITHM, START, END, MAXDEPTH in GRAPH_TABLE syntax
- All 340+ existing tests pass

src/barabadb/query/lexer.nim

@@ -135,6 +135,8 @@ type
     tkEdge
     tkLabels
     tkGraphTable
+    tkCreateGraph
+    tkDropGraph
     tkMatch
     tkColumns
     tkSrc
@@ -362,6 +364,9 @@ const keywords*: Table[string, TokenKind] = {
   "label": tkLabels,
   "labels": tkLabels,
   "graph_table": tkGraphTable,
+  "create_graph": tkCreateGraph,
+  "drop_graph": tkDropGraph,
+  "graph": tkGraph,
   "match": tkMatch,
   "columns": tkColumns,
   "src": tkSrc,
@@ -370,7 +375,6 @@ const keywords*: Table[string, TokenKind] = {
   "matched": tkMatched,
   "array": tkArray,
   "vector": tkVector,
-  "graph": tkGraph,
   "document": tkDocument,
   "similar": tkSimilar,
   "nearest": tkNearest,