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

res/ObsidianDragon.manifest

@@ -5,7 +5,7 @@
   <assemblyIdentity
     type="win32"
     name="DragonX.ObsidianDragon.Wallet"
-    version="1.1.0.0"
+    version="1.1.1.0"
     processorArchitecture="amd64"
   />