fix: macOS block index corruption, dbcache auto-sizing, import key rescan height

- Shutdown: 3-phase stop (wait for RPC stop → SIGTERM → SIGKILL) prevents
  LevelDB flush interruption on macOS/APFS that caused full re-sync on restart
- dbcache: auto-detect RAM and set -dbcache to 12.5% (clamped 450-4096 MB)
  on macOS (sysctl), Linux (sysconf), and Windows (GlobalMemoryStatusEx)
- Import key: pass user-entered start height to z_importkey and trigger
  rescanblockchain from that height for t-key imports
- Bump version to 1.1.1

CMakeLists.txt

@@ -4,7 +4,7 @@
 
 cmake_minimum_required(VERSION 3.20)
 project(ObsidianDragon 
-    VERSION 1.1.0
+    VERSION 1.1.1
     LANGUAGES C CXX
     DESCRIPTION "DragonX Cryptocurrency Wallet"
 )