feat: complete Phase 3 + new production roadmap for Web/ERP

- Thread-safety: locks in LSMTree and Graph engines
- Raft network transport: async TCP, serialization, heartbeat, 3-node election test
- CI/CD: GitHub Actions workflow
- Cleanup: remove dead code, unused imports, build artifacts
- New PLAN.md targeting production Web/ERP readiness
- 216 tests passing

src/barabadb/query/adaptive.nim

@@ -1,7 +1,6 @@
 ## Adaptive Query Execution — runtime query plan adaptation
 import std/tables
 import std/monotimes
-import std/algorithm
 import std/strutils
 
 type

src/barabadb/query/codegen.nim

@@ -1,8 +1,6 @@
 ## Codegen — compile IR plan to storage operations
-import std/tables
 import std/strutils
 import ../query/ir
-import ../core/types
 
 type
   StorageOpKind* = enum