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/baramcp.nim

@@ -0,0 +1,24 @@
+## BaraDB MCP Server — Standalone Entry Point
+##
+## Starts BaraDB in MCP (Model Context Protocol) server mode over STDIO.
+## The server accepts JSON-RPC requests from AI agents and provides
+## tools for SQL query execution, vector search, and schema inspection.
+##
+## Usage:
+##   baramcp --data-dir ./data
+##
+## Environment variables:
+##   BARADB_DATA_DIR — Path to the data directory (default: ./data)
+
+import barabadb/mcp/server
+
+when isMainModule:
+  let dataDir = server.parseDataDir()
+  server.logToStderr("Starting BaraDB MCP Server with data dir: " & dataDir)
+  try:
+    discard server.init(dataDir)
+    server.run()
+  except:
+    server.logToStderr("Fatal error: " & getCurrentExceptionMsg())
+  finally:
+    server.close()